Added some helper methods to check commands
Added attribute count helper
We cannot use these methods in a nice way, so remove them
Added some default instance variables
We allow multiple keys, for example --cat and -c
Added ExecuteableCommand module
The expected attribute count should be an Array or Range, so we can check it when parsing
Added helper method for adding attributes to the list of attributes
Merge pull request #15 from matthiasbeyer/implement_command_class

Added some helper methods to check commands