Clean up Comments - Switch to YARDoc

[mdaines-r7]

Adjust the comments throughout the code to produce useful RDoc. For example, if you visit the gem page (i.e., through http://rubygems.org/gems/nexpose), there is no clear starting point, and it isn't clear that many of the useful methods are actually exposed through the Nexpose::NexposeAPI module's documentation.

When adding new documentation, covert to using YARDoc style.

[mdaines-r7]

This is mostly done. As methods get touched, comments are added.