added HashSet implementation (TODO: find a better name not conflicting with System.Collections.Generic.HashSet)
fixed error in Base.FSharp project-file and updated nuspec; (deployed new package)
renamed HashSet to PersistentHashSet;
[VS2015 port] refactored initialization of generic static readonly fields (Constant, Color, Text) because existing code no longer compiles with VS2015
Merge branch 'VisualStudio2015' into development
Merge branch 'development' of burrow.ra1.vrvis.lan:aardvark/base into development
Merge remote-tracking branch 'remotes/burrow/development'

Conflicts:
	src/Aardvark.Base.FSharp/Aardvark.Base.FSharp.fsproj