fixing pb by using PointListReader and GenericWriter together (operator >>)
fix ppm writer which was not fine
typo correction in doc
add in GenericWriter a template partial specialisation for functor HueShadeColorMap (in order to separate PNM and PGM writer which use different functor scalar-> scalar and Scalar->Color
Cleaning some function doc
Merge pull request #796 from kerautret/FixListReaderUseGenW

fixing pb by using PointListReader and GenericWriter together (operator ...