Investigate bidirectional parsing

[ty-]

Remarks was originally intended as a shorthand representation of xAPI Statements, and the parser for Remarks -> Statements was created to add value to this syntax (why rewrite something you've already essentially written?).

As support for features grow, the syntax is holding its ground. It's worth investigating if it's worth the trouble of supporting bidirectional parsing, so that we can "compress" xAPI Statements into Remarks as well.

If Remarks have even 80% coverage of the spec, this seems both possible and worth it.