avg,lightness,luminosity methods
avg,lightness,luminosity methods added
Dead Quick Links fixed

Except 'About' and 'Installation' all the quick links were dead. Also added 'Virtual Environment' and 'Fedora' to quick links.
Merge pull request #497 from anishchandyoterpa/patch-1

Dead Quick Links fixed. Thanks for keeping us up to date.
Merge branch 'conversion' of github.com:salil93/SimpleCV into salil93-conversion