nested brackets cause issues

[lbellini]

I'm trying to write "initially rotary [[step and fold] ers motivate]"
as soon as I get through "step" sd begins to lag by notable seconds. it may be trying to match on a bunch of possibilties?
Just try it. Weirdness.

[wba4]

This is the same as #71, and has been known for some time. I designed a workaround for it, involving hashing on the first 4 characters of the text that the user has typed. (4 characters is easily enough. and the hash key comes from a 32 bit word.) The change is complex, because we have to take care of things like short strings and optional apostrophes. I didn't want to spend any more time on it, so it was backed out in an unfinished state. The parser is correct and reliable, and I'm going to keep it that way.