Create Prototype RPC For API Reference

This prototype RPC reformats the output of bitcoin-cli help
createrawtransaction, clarifying some of the description and adding a
concrete example.

* The RPC command is the name of the h4 subsection.

* The subsection starts off with a prototype command much like a
  Unix-style manual page.  This prototype gets its own CSS class so we
  can optionally give it a distinctive style

* Each argument to the RPC gets its own h5 subsection. The reformatted
  code from the `help` text gets its own CSS class so we can optionally
  give it a distinctive style.

* The results of the RPC also gets its own h5 subsection and its own
  CSS class.

* I rolled my own real-life testnet example. The examples from
  `help` use placeholder variables which make for less clear
  examples.  Both the commands run and the resulting output get their
  own CSS class.

I haven't styled any of the new CSS classes here; @saivann always has
much better ideas than I do.

Other changes:

* Added div to give APIref the same style as devguide so I could see if
  the code blocks were overflowing the layout.

* Removed reference-style links from devguide and put them in
  _includes/references.md. Then use an {% include %} in both devguide
  and APIref to source that file.

Not done:

* No highlighting applied. Most of the code blocks here don't contain
  actual code---just prototypes---so even if syntax highlighting would
  apply well to these code blocks, it probably won't apply well to all
  of our code blocks.
Update Proto RPC Style / Fix Links

* Replaced all subheadings within a RPC description with bold text. This
  keeps the table of contents clearer and also lets us use more
  descriptive (fake) subheadings. Suggested by @saivann (thanks!)

* Changed all links in _includes/references.md to use full path names to
  /en/developer-guide so they work in the API reference. (Note: this
  breaks our p:hover CSS styling which matched internal links only.)

* Modified _plugins/autocrossref.rb to give all autoxref'd links
  class="auto-link" so we can use the previous styling with a few
  changes to the stylesheet.
Restore auto-ref link CSS styles
Merge pull request #76 from harding/apiprototype

Create Prototype RPC For API Reference