Improve Rake::DSL method documentation
Improve Rake::DSL method documentation

Task definition was inadequately documented.

When built from the gem, the DSL methods did not appear in documentation
as they are marked private.  Now documentation is forced (except for
file_create) which appears to be internal).

taiganakagawa/rake,ipmobiletech/rake,ruby/rake,jaustinhughey/rake,88rabbit/rake,envato/rake,zzak/rake,bentley/rake,askl56/rake,hsbt/rake,utilum/rake,ruby/rake,Vanzct/rake,pjump/rake,codedogfish/rake,hsbt/rake,envato/rake,esasse/rake,tmornini/rake