For some reason, when I cross-compile opusfile on Fedora 23,
I get example binaries with exit immediately without error.

Building them on Fedora 20 (in a docker container) produced
working binaries. Until we figure out what the bug is, include
this for convenience.

The build doesn't actually work because of the 'make check'
steps in the Makefile, which require wine.

For those who would like network access to be a separate step.

This doesn't work in a normal shell, but enables 'make -C mingw'
which is convenient.

Thanks to ron for the suggestion.

This builds win32 versions of the library and examples
on linux using the mingw-gcc cross toolchain and wine.

It also automates downloading and building the
required dependencies. Update the _URL and _SHA
variables to build against newer upstream releases.

Thanks to Ron and Mark Harris for help with the makefile.