lexicon_filter fix for escaped options

Fixes #1703.

Missed that case as the only other escape sequence in the docs previously was `\cd` which had to be trapped differently due to `cd` also being a built-in.

Also, I had been giving a bit of space in the synopsis around short and long options to make them clearer (the effect is more noticeable in the man pages). I've updated the filter to pick up on options tight to `(` or `[`, but it would be better to have a convention one way or the other. I'm happy to run through and update accordingly.