Revisions from review

* Access blue color via standard method rather than extend self on Shoes::DSL
* Adding constants
* Use default parameter on set_style instead of ||= in method body
* TextFontFactory.create_font now takes style hash instead of individual values
* Removing unnecessary require
* Better naming for range determining method in FittedTextLayout
* Clearer name for the left/top methods on FittedTextLayout