- Bump version.
- Remove AC3 renderer. It's not ready.

dev -> dev-1.2.0-rc

dev-1.2.0-rc -> master

Correctly reset ADTSreader state

- This change:

1. Extracts HlsExtractor interface from TsExtractor.
2. Adds AdtsExtractor for AAC/ADTS streams, which turned out to be
   really easy.

Selection of the ADTS extractor relies on seeing the .aac extension.
This is at least guaranteed not to break anything that works already
(since no-one is going to be using .aac as the extension for something
that's not elementary AAC/ADTS).

Issue: #209

Issue: #289

Some extractor implementations underneath MediaExtractor require a seekTo
call after tracks are selected to ensure samples are read from the correct
position. De-duplicating logic was preventing this from happening in some
cases, causing issues like:

#301

Note that seeking all tracks a side effect of track selection sucks if
you already have one or more tracks selected, because it introduces
discontinuities to the already selected tracks. However, in general, it
*is* necessary to specify the position for the track being selected,
because the underlying extractor doesn't have enough information to know
where to start reading from. It can't determine this based on the read
positions of the already selected tracks, because the samples in these
tracks might be very sparse with respect to time.

I think a more optimal fix would be to change the SampleExtractor
interface to receive the current position as an argument to selectTrack.
For our own extractors, we'd seek the newly selected track to that
position, whilst the already enabled tracks would be left in their
current positions (if possible). For FrameworkSampleExtractor we'd
still have no choice but to call seekTo on the extractor to seek all
of the tracks. This solution ends up being more complex though, because:

- The SampleExtractor then needs a way of telling DefaultSampleSource
  which tracks were actually seeked, so that the pendingDiscontinuities
  flags can be set correctly.
- It's a weird API that requires the "current playback position to seek
  only the track being enabled"

So it may not be worth it! I think this fix is definitely good for now,
in any case.

Issue: #301

Previous regular expression for extracting codec information was wrong,
given a line that defines a variant it added information from “CODEC=“
text to the end of the line (including also information about
RESOLUTION or alternate rendition groups as part of the CODEC field).

This is not causing a functional problem (at least known by me)
although is making codecs field storing information that is not related
with the codec.

- Data needs to be unescaped before it's passed to SeiReader.
- SeiReader should loop over potentially multiple child messages.
- I also changed the sample passed to the EIA-608 renderer so that
  it's the entire sei message payload. The first 8 bytes are
  unnecessary, but it seems nicer conceptually to do it this way.

Issue: #295

1.2.2 release

1. Clear prefixFlags when a NAL unit is found.
2. continueBuffering should return true if loading is finished.

Merge minor release 1.2.3