Generic `ctcp()` bot method

[dgw]

Requested Feature

Exactly what the title says. Sopel should have a "nice" way to send non-ACTION CTCPs. We already have the plugin decorator to handle incoming ones, after all.

Problems Solved

We have bot.action() for the most common case, but anything else has to go through bot.write() (and the plugin author must learn the vagaries of formatting CTCP command strings on their own).

Alternatives

As mentioned above, using bot.write() with hand-crafted strings.

Notes

No response