Working version!

Here is a very basic working version of `libAV.jl`.  It's not pretty and needs work, but I wanted to at least put it out there, and get comments and thoughts about moving forward.

#### Notes
1. Works with libav-0.8.  It will probably work with the corresponding version of ffmpeg. No `BinDeps.jl` support yet.
3. Includes a minimal working video player (`examples/tutorial/libav-0.8/tutorial01.jl`), based off of
  * http://dranger.com/ffmpeg/tutorial01.html
  * https://github.com/chelyaev/ffmpeg-tutorial.
4. Includes an updated `wrap_libav.jl` script
  * Rewrites functions with conversions to make calling easier.
  * Additional edits/additions/rearrangements made by hand.
  * No nice API yet--everything is done with calls to the library.
5. All structs are currently immutable.

I'm not sure if the last point is strictly necessary, but that was the state it was in when I finally got things to work.

Isaiah, are you still interested in working on/maintaining this?  If so, (or even if not):

1. Issues are not enabled on your repository.
2. It should probably be renamed.  Possibilities: `LibAV.jl`, `AV.jl`, ... Since it also should work with ffmpeg (and because of the animosity between some people in each project), something other than libav might be better, but I don't care much.
3. I added an MIT Licence here.  I'll assume that's okay?  (It feels strange to have a license on wrapped code, but there are some hand edits, and a nicer interface eventually.)

Separately, once this has a home with issues enabled, it would be good to talk about interface design with interested parties.

cc: @timholy, @glenn-sweeney, @lucasb-eyer
ref: https://github.com/timholy/Images.jl/issues/96