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)