Add LoopTok for loop statements storage
Add tests for for loop expressions
Add parser for for loop expressions
Add test for renderTemplate transform of for loops
Change mergeMap to accept a HashMap as an argument

This is just so the top level varTable isn't used as the default HashMap for
replacing Token names.
Add loopParser for handling for loop syntax
Merge branch 'expression/for'

First basic handling of for loop expression. This doesn't allow other
expression — like if expression — handling inside the body of a for loop.