Finish generic color and unit arithemetic
Create a development profile

Having a development profile is a great place for examples and
expirementation. It's also nice because it provides a safe place to put
data_readers.clj (which isn't a good idea to package with the jar).
Update the garden.core doc string
Minor cleanup
Add note about refering garden.arithemetic operators

Refering the garden.arithemetic operators causes Clojure to issue
warnings about symbols being replaced. Commenting out the line makes
them go away.