Updating identifiers syntax with back-quoted identifiers in CLS

This is to resolve possible name clashes with all the different keywords in Coral – quoted identifiers are never treated as keywords.
Revisiting function and method types in CLS

Changing syntax of function type declarations from:
def function_name (args : types) -> return_type
To:
def function_name (args : types): return_type
Where surprisingly, return type may look like:
(type) -> type.
Updating keywords in CLS

Adding: get, set, weak, singleton-type, implicit, step