Added tests for checking Draft 3 values for string format
Now tests.py can also run optional JSON tests
Added validation for Draft 3 values for string format
Removed "INCLUDE_OPTIONAL" constant in tests.py
Separated "format" validation into its own class
More format tests added
Removed Validator subclass, added FormatChecker class and sample subclasses
Added CssColorChecker as an example that uses more than regex for validation
Added documentation for format checking
Added docstring for the FormatChecker.conforms() method
Fixed RST "note" format
Allow individual files of optional tests to be specified. Updated README.md
Replaced FormatChecker subclasses with a decorator to register checker functions
Removed FormatChecker subclasses from documentation
Improved format checking for ip-address, ipv6 and CSS colors
Opt out of unwanted formats
All "host-name" and "regex" format tests passing
Python is terrible.

Enable the optional tests, and fix the stupid bug with longs by drilling a long
hole through my brain.
Docstring wording.
Test format error message.