Add support for V_PRED 

Wraps the libaom highbd_v_predictor

rav1repl: add exit+quit commands

Don't rebuild unnecessarily.

Native rust h_pred implementation

Upgrade dependencies, use less strict bounds

Since it is not visible outside of test

Replace od_icdf() usage with actual constants.

Add extremely basic RDO

The only calls to od_icdf() use constants so this function is
 unnecessary and can be deleted.

On a rescaled 192x64 version of akiyo_qcif this reduces file size by
~10% for a ~.3 dB loss on PSNR.

- Only chooses between DC_PRED and H_PRED at the superblock level
- Distortion is just SSE
- Uses floating-point math for no reason

Test the entropy encoder

intra_mode_ind is no longer used

Leverage the aom reader.

Make the --output parameter mandatory.

Fix the example command line parameter.

Drop the --release parameter from cargo so it builds faster.

Move pred_dc_4x4 to testing namespace

Since it is only available for testing.

Add Travis build status badge.

Fix command line

Change the rav1e command line to take an option -o OUTPUT to match every
 other encoder.
If no output is specified, it will write to stdout.

The encoder now prints status to stderr instead of stdout.

Use a Box<Write> instead of File for the output_file field of
 EncoderFiles.
This matches the input_file: Box<Read> field.

Implement a pure-rust pred_dc

And add some tests.

Fix #2: Enable Travis