Gecko Media Rust Crate

Firefox's Media stack in a Rust crate.

Build with cargo build.

Run tests with cargo test.

A minimalistic player is also available:

$ cd examples
$ cargo run --bin test-player -- /path/to/some/audio-file.ogg

Procedure to update the imported code from Gecko

A mozilla-central Gecko build is required. Optimizations and debug should be enabled. Example mozconfig file:
```
ac_add_options --enable-optimize 
ac_add_options --enable-debug 
```
The import script has to be executed from the gecko-media directory:
```
$ cd gecko-media
$ python3 import.py /path/to/mozilla-central gecko/
```
The gecko-media/gecko/src and gecko-media/gecko/include directories content will be removed and the source and header files declared in gecko-media/data/*.json will be copied back to those two directories.
The import script will create a subfolder inside glue_diffs/ named with the upstream revision number you are updating to (i.e. glue_diffs/392049:f41930a869a8/). Inside this subfolder you may find a series of diff files. You need to apply these patches manually to the code inside gecko-media/gecko/glue. Some context about why this is needed can be found in this issue.
Fix potential build errors!