(PDOC-17) Add support for YARD tags in puppet code

Prior to this commit, most of the HTML created for documenting
puppet code was auto-generated by YARD, meaning that it was not
always presented in a way that was consistent or easy to read. 

Now we are explicitly defining the HTML and styling that we want
to use when generating documentation for defined types and classes.
This means that we can define exactly how we want the output to look
so that is more compatible with puppet code.

I have yet to add links to any of the details around parameters because it's
not clear to me where those links should go at the moment. It should be
simple to add them though when we decide what we want them to look like.
Do you know if it's possible to override only one aspect of this section (i.e. what if I wanted the way the @return tag looks to be slightly different than what YARD does by default) without rewriting the whole thing? I had assumed that this whole section would have to be overwritten in order to make modifications (but I could be totally wrong I was just guessing).

I had kind of reimplemented this thinking that we may want things to look a bit different than the way YARD generates HTML for certain tags. Although in retrospect it is pretty much the same, so I think I can remove a lot of redundant code for now. Thanks for pointing that out!