Rename default_config.py to config.py

The next commit will (among many, many other things) add other config-related things to the newly renamed config.py.
Fix connections over TLS.

YAY~! Finally! :D
This is definitely one of the biggest milestones so far!
We are by /no means/ finished—not even /close./ There are still several /major/ issues—
    She only really works under ideal conditions and dies from an exception
      if pretty much anything goes wrong.
    She's pretty bad at reporting errors, just letting Python dump tracebacks
      to stderr rather than printing more relevant information.
    She still doesn't really /do/ anything.
—but at least she /connects./ That's more than you can say for previous versions.

Mane changes:
    Added a (hacky and bad) way to convert between the `ssl` module's
      TLS version constants and meaningful strings (e.g. "TLS 1.2", "SSL 3").
    Added a lock for the in-memory config.
    Made the Connection constructor take references to the config lock
      and the global HandlerManager, instead of the name of the config dir.
    Moved dump|load-config code to lunabot.config.dump() and lunabot.config.load().
      These use lunabot.config's attributes instead of taking and returning
      references to the config.
    Moved the create-config-dir code to lunabot.config.dump().
    Added the very-much-missing "host" suboption to the default config.
    Canterlocked the name of the default config as per PEP 0008.
    Made main() set the path to the config dir as an attribute (lunabot.config.dir).
    Added more TLS options to the config.
    Made the argument parser use ~/.lunabot as the default config dir.
    Made configurable paths be interpreted relative to the config dir.

And, of course, I littered TODO comments all over the place. :P
'cause, like I said: there's still a ton of work to do.