ENH : imported ffmpeg_reader

Imported code from moviepy (https://github.com/Zulko/moviepy)
with permission
ENH : draft of high-level code for rewindable stream classes
ENH : directly using ffmpeg

first pass at getting ffmpeg_reader working under new ABC
ENH : renamed + process_func in new ffmpeg
fixed typo in base_frames

re-worked FrameRewindableStream.__getitem__ to not raise exceptions
on definition by adding a helper generator function.
CLN: Simplify API logic.
WIP: Start work on better API. Video works. TiffStack has standin code.
TST: Update tests. Replace bw ref. frames with color.
REF: Decode the video into a tempfile.
REF: FFmpegVideoReader is a FramesSequence

Parse ffmpeg stderr in same pass.
Merge pull request #1 from danielballan/api

Api + ffmpeg re-write
ENH : negative indexing

Added support for conventional negative indexing

Error-check input to make sure data is in range.
TST : negative index

Only a 'does it blow up test'
ENH : added import logic on tiff stacks

Will now try to import first libtiff then PIL/PILLOW based tiffstack
readers.
CLN : removed debugging print statement
Merge pull request #34 from tacaswell/ffmpeg_iter

Ffmpeg iter