Adding support for custom comment pattern specification

This is initial enhancement to support the following issue readmeio/oas#603.

This enhancement:

• added an optional pattern argument command-line argument with help text
• added pattern attribute and get/set methods to Options object
• added loadPattern method to Loader to load json file that contains specification of pattern
• added section in swaggerInline in index file to handle adding the loaded pattern file to the options variable
• ensured backwards compatibility if no pattern is specified
• expanded test coverage to cover all changes

Testing

Refer to the can extract comments from custom pattern and custom file test in the extractor.test.js file to see a detailed test of the additional functionality.