Created `Motion::Speech::Utterance` providing custom initialization
Refactored so `Utterance` provides the :to_speakable interface instead of `Speaker` itself

Move more of the customization logic down to the utterance instead of
all in the speaker
Easy customization of the utterance rate with symbol options
Easy customization of the utterance pitch
Easy customization of utterance voice
Easy customization of the utterance volume
No reason to store options hash in Speaker since it is only passed to an Utterance
Fixed typo in README
Merge pull request #2 from macfanatic/customizations

Customizations