Enhancements and Fixes around `Uri` implementation

1. Some changes to be able to render an URI definition as String (belongs to issue #23).
2. Renamed `NumericParam` to `NumericPathVar`, `IntParam` to `IntVar` and `LongParam` to `LongVar` (belongs to issue #22 ).
3. Updated Scala to version **2.11.1**
4. Regard an optional fragment identifier in a URI definition (belongs to issue #26)
I'm not sure I like this factory method. It appears over complex (what if, for some strange reason, someone calls it with multiple options?) and only exists to help the parser. (Also commented on below)