Support a file that uses helmsman having an extension

[beaugunderson]

It looks like prefix gets set incorrectly if the main file using helmsman is named with an extension. For example, a file named projects.js gets a prefix of projects.js-, which is incorrect.

[mattmcmanus]

Gross! I'll fix that soon.

If you're feeling inspired, the code for that is here

[beaugunderson]

I've added fixes for the three issues I've created here in my fork:

https://github.com/beaugunderson/node-helmsman/compare/mattmcmanus:master...master?w=1

In addition to those changes I am also considering adding support for a non-require pattern, where you can specify the usage information in the main file (this will be useful for including commands of other languages, for example)... Is that something you're interested in?

[mattmcmanus]

Whoa! Awesome dude. All three issues taken care of AND fixing my spelling errors

If it is at all possible, could you open two separate pull requests? One for the file extension issues #3 & #4 and a separate one for the PATH + exports checking? The latter is a bigger shift from how things are now and I want to make sure to take the time to go through the changes there.

Thank you @beaugunderson. This is awesome work.

[beaugunderson]

Attempting to split up the changes now. :)