Optimize some CodecCounter inefficiency.

1. Use ints rather than longs.
2. Remove some counters that dont seem hugely useful.
3. Replace use of volatile with explicit method calls that
   cause a memory barrier. This is a lot more efficient than
   using volatile because it can be invoked only once per
   doSomeWork.
Minor cleanup.

- Add constants class. Currently housing a single lonely variable,
which is used generally throughout the library, and so no longer
nicely fits into a specific class.

- Rename a few other constants to add clear units.

- Made minor tweak to ExoPlayer documentation.
Simplify parsing of encryption data + support SENC boxes.

Issue: #4
Optimize out quite a few allocations in FragmentedMp4Parser.
Don't release AudioTrack unless we have to.
Remove unnecessary SuppressWarning annotations.
Add missing C file.
Fix bug introduced supporting self-contained media chunks.

The equals check we perform needs to ignore the max dimensions.
This tended to work in practice because formats would be the
same object, but in the case where different format objects
are used, things can break.
Support chunked requests.
Bump version to 1.0.12.
Fix the build.