Add option to specify external rules file

[m8ttyB]

To allow for a diversity of configuration options, add an option to specify and use an external file containing a list of rules to run checks against.

As a first pass, let's use --rules as the command-line specifier.

[kimberlythegeek]

Along the lines of #45 , I'm not sure this is needed. Deque does a good job of both coverage and configuration options in the aXe API.

@m8ttyB thoughts?

[m8ttyB]

Yes, close it! Our knowledge and understanding has come a long way since August.

[kimberlythegeek]

It has indeed :)