Update avcodecs.py

propose to use libvpx instead of vp8 for webm video encoding (see here: http://ffmpeg.org/trac/ffmpeg/wiki/vpxEncodingGuide)
Merge pull request #26 from ouhouhsami/patch-1

Update avcodecs.py
add authors file
updated and renamed README.txt to README.md

Also added the Travis build status image and a reference to the
AUTHORS.txt file.
bump version to 1.1.0