Add enum factory
fixes #5
fixes #6, add UniqueFactory;
fixes #3, add SetFactory
fixes #4
Merge remote-tracking branch 'remotes/origin/feature_arrayfactory'
Merge remote-tracking branch 'remotes/origin/feature_enumfactory'
Merge remote-tracking branch 'remotes/origin/feature_uniquefactory'

Conflicts:
	NDummy.Tests/NDummy.Tests.csproj
	NDummy/IArrayFactory.cs
apply fix_nonintegral_sequence_factory and merge feature_arrayfactory, feature_enumfactory and feature_uniquefactory branches