tweak gemspec
Loosen requirement for video bitrate in transcoder spec.

Since latest ffmpeg appears to be extremely liberal in using VBR.
Rake version 10 in gemspec.
Note on ruby compatibility in README.
Remove ffmpeg 0.7 support.
My own implementation of io timeout hack.

- greatly simplified
- avoid spawning a new thread for each line of output
- should therefore use less cpu and memory
- removed ruby 1.8 support hacks
More info on ruby implementation compatibility.
changelog
whitespace
Ensure timeout thread is killed.
Ignore .rbx.
Ruby 1.9 hash syntax!
prefer unless nil over if nil.nil?
prefer nil || something over weird ternary
Avoid including leading space in video/audio-streams.
remove comment mentioning old ffmpeg version
remove unused last_output variable
Remove unsupported codec check while transcoding.

Because:
- the code path was not reachable due to each-lining breaking on 'r'
- never seen ffmpeg say unsupported codec while transcoding myself
- the reason for the check is unknown (originally written by @stakach)
Have transcoder break line on 'frame=' rather than 'r'.

- r had unclear purpose (originally cargo culted)
- actually split every line into to two (fRame and bitRate)
no need to namespace FFMPEG::Error inside the FFMPEG module