Added required filtering/delay/memory to get continuation

Continuation matches Python code now

Build tests in the tests/ directory instead of top, cleanup, rename,
and eliminate recursive make for the celt/ unit tests.

by POSIX. The other _t types that are not part of the API are still there
for now. Also, got rid of all that was left of the 64-bit types.

Also, added an Ogg encoder (doesn't work quite yet).