Implemented slice assignment

Note: untested due to typechecker issue.
Implemented "has"

Note: since tuple loose field names, has does not yet behave as expect
on tuple-related types.
Implemented "is"
Implemented get/set-annotation.
Another round of further systematization of names in RascalPrimitives
__getInterrupt -> isInterrupted
Working on overloading: use of the type checker info relevant to
overloading.
Added code that adds the 'testsuite' function to the muRascal code;
necessary to run tests written in the muRascal language.
Made str_add_str n-ary for the benefit of string templates.
Pushed function types down to the RVM interpreter.
Updated the RVM interpreter examples.
Fix: 'equal_type_type' -> 'type_equal_type' in one of the test examples.
Added a file to test the test framework.
Half way with string templates
Merge branch 'master' of https://github.com/cwi-swat/rascal.git
Refactored the RVM interpreter 'executeProgram'; added 'executeFunction'
that invokes function instances.
String templates mostly implemented.
Still to do:
- testing
- indentation
On special request: SendMoreMoney.
Merge branch 'master' of https://github.com/cwi-swat/rascal.git
New insight and respective fix to the recent refactoring of the RVM
interpreter 'executeProgram'.