tweak jenkins emoticons
clean up eval a bit
clean up airbrake plugin a bit
standardize use of rescue in plugins
fix isitdown plugin
remove need for class logger in Plugin
privatize regex (use match?)
Shift some logic

Much of Dispatchable#dispatch is now in Plugin#execute_on. This puts the
logic where it can more easily access Plugin instance variables and
handle execution -- also decreases the number or arguments and removes
the external handling of MatchData.