Auto Cross-Reference Proof Of Concept

New plugin which can automatically add cross-references to blocks of
Markdown.
Only match on word boundaries (suggested by @saivann)
Move cross ref defs to separate file
Test autocrossref on technical section

Tried testing autocrossref on a technical section, and discovered one
bug (now fixed).  With this test done, I think it might be time to merge
this into the full tree.  Changes:

* Changed word boundry (\b) in regex to more complicated form that just
  doesn't match inside words. This makes \`term\` work.

* Added autocrossref to P2PH script eval section, a technical section.
  With the above fix, it works well.

* Added a few more terms to the YAML list for the P2PH script
  eval section.
Only display links on p:hover (suggested by @saivann)
Apply consistent link styles
Merge pull request #1 from saivann/devautocrossref

Apply consistent link styles
Merge pull request #51 from harding/autocrossref

Auto Cross-Reference Proof Of Concept

Confirmed it Jekyll compiles with @instagibbs's OpMode commits, so merging after 24 hours notice.  I plan two more pull reqs: a medium-sized diff to apply autocrossrefs to each section, and a huge diff to remove the old manual formatting.