Merge pull request #1 from llambeau/master

Thanks!
Add SeqType.
Add SetType.
Move non-first-class abstractions under support/
Factorize common code through a CollectionType helper module.
Factorize iteration strategy through a UpHandler helper.
Start Realm abstraction.
Rename and refactor UserType as AdType and document it.
Add a RealmBuilder tool.
Authorize relation(TupleType) in RealmBuilder's DSL
Replace RubyDSL by Realm itself, through DSL delegation to Builder.
Add Heading#empty?
Simplify RealmBuilder, remove the stack-based feature.
Start concrete Q syntax.
Extend RealmBuilder to also act as a factory.
Refactor RealmBuilder as a simpler TypeFactory.
Add support for named constraints in the concrete syntax.
Move unit tests under spec/unit.
Add support for Range/Regexp/Block subtypes in factory.
Add type builder DSL on Qrb module itself.