Minor changes to fix Javadoc.

- cache ref didn't work because it referred to a private variable
  (which isn't documented) from a public interface definition
  (which is). Meaning the Javadoc generator was trying to link
  to documentation that didn't exist.
Tighten isReady() up again.
- Bring back requirement for the first video frame to be rendered
  before isReady returns true, *unless* we've deduced that the
  upstream source is serving multiple renderers.
- Ditto for requiring that the audio track has some buffered data.
Make audio renderer more robust to bad getTimestamp values.
Call FormatHolder what it really is.

Since we have a Format class as well, it's very confusing that
FormatHolder actually holds a MediaFormat. I think it's quite
likely that Format will need promoting into the root package as
part of the HLS work, which will make this even more confusing
(although it is possible that for HLS we'll define yet another
Format class, if it turns out we need significantly different
fields).

Note - I deliberately avoided renaming the formatHolder
args/params, because they're not particularly ambiguous and
because it introduces some ugly line breaks.
Add disclaimer to stop people getting confused by the minSdkVersion.

Issue: #31
Don't try and read a trackEncryptionBox unless we actually have a saiz atom to parse.

Issue: #35
Fix potential cause of infinite-spinner-without-failure.
It looks like for the case of self-contained media segments,
it's possible to get stuck without failure in the case that
the load fails having loaded less than the length of the init
data.
Add https->http redirect sample video.
Make MediaCodecTrackRenderer discard non-keyframes after seek.
This means that after a decoder flush, the renderer will avoid
feeding non-keyframes into the decoder until it has received and
fed the first keyframe. The decoder has no way of correctly
decoding non-keyframes that arrive before a keyframe.
Parse some DASH manifest components for DVB LIVE.
Merge fMP4/H264 and WebM/VP9 DASH implementations.
Fixed MPD date/time parsing issue.
Make SmoothStreaming manifest more robust.
- Skips unrecognized elements rather than crashing.
- FourCC treated as required for video and optional elsewhere,
  as per the SmoothStreaming spec.
- Only parse initData text when we're actually in the ProtectionHeader element
Bump version to 1.0.13.