Added equals function to check for equality between commands.
Currently, it will check if the commands had the same user input string
Changed Command class such that:
it now accepts a primary command for show.
it is now able to handle no primary argument for show.
It is now able to handle no primary argument for the other commands
Improved on parser in general.
Refactored method Parse(String) to parse(String)
Added some unit tests for Parser class