use ruby 2.0.0 for development 
use a more recent version of ZenTest (4.8.1 would not install) 

$ bundle update ZenTest
fix : Bundler complains unless you use a url ('https://rubygems.org') as source
update README with updated instructions to install dependencies (sox)
add doc for developers
use sox instead of lame + soundstretch
use markdown for README
Merge pull request #1 from alainravet/use_sox

replace lame+soundstretch by sox