Recoverable Errors

[tohrnii]

We should add recoverable errors to the parser to recover all errors while parsing instead of terminating on encountering the first error.

[bobbinth]

@bitwalker - I think we already have this? If so, we should probably close this issue.

[bitwalker]

We've relaxed the parser a bit, and removed some of the hard errors, but a few things are still hard errors that stop parsing. We would need to use the error recovery features in LALRPOP to make parsing complete before raising errors. We're pretty much set up for it now, just requires some modifications to the grammar file and AST to store error nodes.