Added "_" prefix to protocols
renamed all types; exposed context;
Merge branch 'develop' of github.com:DAlOG/Parus into develop
Moved VFL implementation to PVVFLImp
Update README.md

Added 2 basic examples, single constraint and VFL
Update README.md
Merge branch 'develop' into group-support

Conflicts:
	Parus.xcodeproj/project.pbxproj
Reorganize code

Add separated groups, add common header.