typos and cosmetique
add sonar link; fix typos
Update readme.md
add a development section
Merge branch 'master' of https://github.com/mpatric/mp3agic

# By Jan-Hendrik Peters
# Via Jan-Hendrik Peters
* 'master' of https://github.com/mpatric/mp3agic:
  add a development section
  Update readme.md
  add sonar link; fix typos
  typos and cosmetique