Added basic types to support AVI container format.
updated avi codec
Added AVI specification doc.
Merge branch 'dev' into codec-avi

Conflicts:
	source/NSynth/NSynth.csproj
initial refactor of overall MediaEncoder/MediaDecoder flow and layout. Removal of all constructors that take Streams and reworking of the way the Open method works
continued refactor.
Cleaned up some stuff left over from changing over the media decoder/encoder structure.
Updated container base class.
Fixed issues preventing TGA and PNG source filters from properly functioning.
Merge branch 'dev' into codec-avi

Conflicts:
	source/NSynth/NSynth.csproj
Merge branch 'codec-avi' of https://github.com/cathode/nsynth into codec-avi

Conflicts:
	source/NSynth/NSynth.csproj
Refactored container API so that it uses the uniform MediaEncoder/MediaDecoder base classes.
etc.
Merge branch 'codec-avi' into dev