Revert "add User#authenticated? as an alias for User#authed?"

Adding as many aliases as one can think of is a terrible trend.

This reverts commit 426c92327212225d504ed0a620c51ceddd4001dd.

Conflicts:
	lib/cinch/user.rb
changelog
move color stripping to Cinch::Utilities::String
documentation fixes
remove Urban Dictionary example

There's a proper gem called cinch-urbandictionary, there's no need to
duplicate it here.
bump version to 2.1.0