Fix .configure use of @config instead of .config.

Otherwise, attempting to use `.configure` without having called
`.config` first will fail, as `@config` won't exist.
[#3,#4] Implement logging, recovering from bad things.

Implement basic logging, set using LOG_LEVEL env var. Rescue IMAP and
Redis errors, logging and waiting for next loop. Thus, Redimap run
eternally shouldn't come crashing down if there's a temporary problem.
On the flipside, the logs must be checked for valid credentials;
otherwise, Redimap will just keep trying repeatedly.

This all feels a bit simplistic, but is a lot better than nothing. ;)
[#9] Improve Gemspec description, including homepage.

Also update README with equivalent information.
Bump version to v0.3.0.
Merge branch 'release/v0.3.0'