Update MetaModelica Documentation

[Martin Sjölund]

There are a number of new MetaModelica features that have (possibly) not been fully documented in the design:

• input output function variables: #3709
• Parametrized uniontypes #3573
• Closures (from Modelica)
• isPresent (from Modelica 2.x)
• Loops and list reductions (?)
• Matching on enumerations (?) #3006
• Matching on constants #3005
• Destructive and dangerous operations: listSetRest (like lisp setcdr), listReverseInPlace, stringGetNoBoundsChecking, arrayCreateNoInit, arrayUpdateNoBoundsChecking, arrayGetNoBoundsChecking
• Add the continue statement in loops #2897
• Implement try/catch: #2887
• Implement try/catch for stackoverflow (special annotation on try/catch): #2090
• Implement threaded iterators: #2816 (not multi-threading, but threading iterators together)
• Support myRecord.x := exp, etc in some cases