This adds support for accessing any binary metadata at the end of
 the comment header, as first specified in
 <https://tools.ietf.org/html/draft-ietf-codec-oggopus-05>.
It also allows the data to be set and preserves the data when
 doing deep copies.

This was meant to affect file opening only, not stream info
 printing.

It seems somewhat silly to have to write your own strcasecmp to
 satisfy the usage pattern found in opusfile_example: scanning the
 whole tags list and handling certain tags specially (as opposed to
 searching for specific tags, as opus_tags_query() does).
Given that we were already using an equivalent function internally
 to implement opus_tags_query, just expose it directly.

This allows the application to report details about the server for
 HTTP[S] streams.
For all HTTP[S], this includes the server software, content-type,
 and whether or not it's using HTTPS.
For live streams, it also includes the station name, description,
 genre, homepage, nominal bitrate, and whether or not it's publicly
 listed.

- Reject 'not a character' values 0xFFFE and 0xFFFF.
- Remove some unnecessary string length checks.

This makes it easier for applications to support album art.
This is still relatively untested.

As requested here:
http://www.hydrogenaudio.org/forums/index.php?showtopic=101817

The main motivation for this is it ensures the files will actually be
rebuilt if the configuration options are changed.

This reverts commit 4e06a90e.
We don't need this if we always build libopusurl.

This makes it more likely the WAV file header matches the amount of
 data actually written if we run out of space.
This is easier than making the accounting better.

a7c5b93c flipped the argument to it from true to false, since it
 made certificate checking actually work.
This commit removes the option entirely to avoid encouraging people
 to use it now that that checking does work.

seeking_example still disables checking (since it's not really
 needed).

We weren't loading the default certificate store, so there were no
 trusted certificates to validate hosts with, and all checks would
 fail (unless explicitly disabled with
 OP_SSL_SKIP_CERTIFICATE_CHECK(0)).
This adds that call, and also adds hostname verification (which
 OpenSSL does not do for us, because they are morons).
I've done my best to get the latter right by reading the RFCs, but
 this stuff is complex, it's easy to make mistakes, and I only have
 a limited ability to test it, so caveat emptor.

This changes op_read_func to
a) Take a single byte count to read instead of an "item" count
    (which the http backend couldn't properly support anyway).
b) Use integers for buffer sizes to avoid having to worry about
    sign differences and whether size_t is larger or smaller than
    opus_int64, etc.
c) Return an explicit error code (instead of using errno like
    fread).
   We had already eliminated the use of errno, but we did it by
    treating read errors and EOF identically in all cases.
   This was preventing us from reporting SSL truncation attacks
    from the https backend.
   The https backend now properly reports such errors.

This commit also fixes a bug introduced in 9b57b0c2, where we
 accidentally started passing absolute offsets to the _boundary
 parameter of op_get_next_page() instead of relative offsets.
We now use absolute offsets in all places, as it is the simpler
 choice.
This matters now, because the error reported when encountering EOF
 before hitting the _boundary is no longer suppressed (but instead
 reported as OP_EBADLINK).

Finally, it removes the op_page_seek() function.
Except for the time needed to decode forward after seeking, this
 function was identical in performance to op_pcm_seek(), and Opus
 requires decoding 80 ms of data after seek anyway, so the relative
 benefit is much smaller than with Vorbis.
A survey of open-source code using libvorbisfile showed that the
 only usages of ov_page_seek() in the wild were calling it to seek
 to the start of the stream, for which op_pcm_seek() already has a
 special case that makes it just as fast.

The documentation was also updated to describe all of these chanes.

This is an incompatible API change.

Right now we have no way to add any more parameters beyond a set of
 basic binary flags.
This unifies op_url_stream_create() and
 op_url_stream_create_with_proxy() into a single function that
 takes a variable-length list of arguments, which can be extended
 in the future to include more options of any type.

This is an incompatible API change.

* Tags were being freed even if not initialized if
   op_fetch_headers() failed on the first link.
  The logic for handling completely empty links would leak, also.
* Ignore fragment identifiers in http URLs instead of rejecting
   them.
* Get the current link in seeking_example's verify_seek when
   op_read_native() fails to return it for us.

This displays the current raw position, PCM position, and
 instantaneous bitrate once per second of output.
This is useful when testing against long-running streams.

This makes it more useful for testing invalid files, where the goal
 is merely not to crash, assert, or trip valgrind warnings.

* s/op_read_stereo_float/op_read_float_stereo/ for the fixed-point
   API.
* Fix compiler warnings exposed when optimizations are enabled.
* Fix opusfile_example to work with --enable-fixed-point
   --disable-float
* Fix seeking_example to not re-define OP_FIXED_POINT if it's
   already been defined.

It's served its purpose, and isn't worth the time it takes now.
Leaving the code around to make it easy to re-enable if necessary.

Also fixes some indenting in opusfile_example.

This is pretty preliminary for now.
Seeking performance isn't great, and there's no caching.
I'm sure there's also lots of bugs.

When a match fails, the index of the position in the link needs to
 be 64 bits.

1) Check for allocation failure and fall back to merely scanning a
 file for consistent timestamps instead of loading it to RAM.
2) Report holes, but do not quit scanning/loading unless they cause
 a discontinuity in the timestamps.

This matches the convention used by opus itself, where
headers are included without a prefix, and the build
must do -I/path/to/opus to find the appropriate versions.

Move this out of opusfile_example and into the API proper.

Seeking and playback work, at least as far as the examples test
 them.
There are probably still lots of bugs.