Added Configuration class

This will allow us to test the intitialization of configuration
Rename "Config" to "CONFIG"

It's a near universal convention in Ruby that constants are all upper
case, with PascalCase resevered for Class and Module names. Having the
configuration information saved in a constant with Pascal case makes the
code less clear to programmers who are used to this convention.
Extend self rather than wrapping methods in block
Merge pull request #56 from flexminder/add_configuration_class

Add configuration class