split out parser into its own well tested module

[bcoe]

I've split out the parser into a stand-alone module that handles the configuration bits for us:

See: #352

You can turn on and off parsing features by using the yargs stanza in package.json:

{
  "name": "my-module",
  "yargs": {
     "camel-case-expansion": false
  }
}

@nexdrew addressing your comments in yargs/yargs-parser#1, yargs-parser allows you to configure the cwd which is the approach I was thinking of for loading configuration appropriately.

I'd love to really dial in how the heck we handle loading configuration appropriately in the various contexts:

• testing yargs-parser and yargs with npm link.
• running libraries locally that have yargs or yargs-parser as a dependency.
• running libraries that have been installed globally with -g.

We are trying to solve similar problems with loading a default version from package.json, I wonder if there's room for a clever module here -- I bet we can extend on some of the work Sindresorhus has done (his use-case is slightly different since he can be confident AVA is installed as a development dependency, and is run in the context of a directory, i.e., is not installed globally).

Reviewers: @nexdrew, @lrlna

[bcoe]

I'm going to go ahead and merge this, @nexdrew feel free to make some edits to the documentation in a future pull request.

I've fixed the issues making Windows tests flaky in another pull request.