Add configuration for brace matching.

[superfell]

It'd be useful to be able to configure the brace matching, including which characters to count as braces, and to be able to disable the beep on a mismatch.

[superfell]

If this is something you'd be interested in accepting, I can look at putting together a PR for it.

[shysaur]

This is certainly a good idea, so if you have the time feel free to contribute with a PR.