In Ruby, identifiers can end with a `!` or `?` too, which means that `class!` or `end?`are not actually keywords, but regular identifiers. This fixes that by not using `\b` but `[^0-9A-Za-z_!?]` instead in some places.
This commit allows using the <semicolon> expansion in commands, instead
of `\;`.
It makes commands look more elegant, and prevents new-comers from
falling into the trap of using <a-;> without escaping the semicolon.
