Input api issues

I had a few issues using bracket-lib dealing with the Input API. Mostly because I assumed `ctx.key` represents all/most of the ascii character set at least, but it seems a bit lacking. For example when I input things like ">" and "<" (common up-stair/down-stair keys) the `ctx.key` never gets populated by anything. I think adding something that corresponds to the ascii character would help here - for example `ctx.ch` which returns a `char`. This would also be helpful for text input.

Just an idea. I eventually implemented input using `INPUT.lock()` which seemed to work much better, but took a bit more boilerplate.