introducing a tutorial for the retina model
adding retina tutorial
updated tutorial, need spell check, validation, nicer images and a discussion on parameters
updated tutorial, rapid spell check, retina parameters discussion added
added retina code tutorial
updated first image sample
minor update
minor updates for doc redirections and tutorial images size
updated retina interface for cleaner use, following OpenCV standards
forgot method name update
activated parallelized gradient computation
Merge pull request #1 from albenoit/retina_devel_newinterface

Retina devel newinterface
updated tutorial with new retina interface use
Merge pull request #2 from albenoit/retina_devel

Retina devel
updated comments and new retina interface use
minor chnges for conflict removal
resolved conflicts, updated retina class interface and optimized a heavy retinacolor process
updated doc
corrections required for portability. To be validated by buildbot
updated doc and interface code to solve compile warnings and errors