renaming all the AST nodes to no longer use underscores in their names
(makes things more Pyret-like)
fix bug where repeated calls to tokenizer will start in a stale state, leading to potential parse failures in the 2nd and later interations of the REPL
Adding standalone contract syntax, with slightly relaxed the requirement for parens around arrow annotations, and just discarding the parsed results in the resolve-names phase of compilation.  Also, revising the syntax for refinement types slightly, to prevent ambiguities in parsing.
Merge branch 'new-world' of github.com:brownplt/pyret-lang into new-world
Merge branch 'new-world' of github.com:brownplt/pyret-lang into new-world
new phase0 snapshot