Add some cross-references
Merge remote-tracking branch 'saivann/dev' into terms

Conflicts:
	en/developer-guide.md
opmodes
slight editing
Add image for @instagibbs
Merge pull request #3 from harding/heightdepth

Add image for @instagibbs
Shorten a few titles
Merge pull request #48 from saivann/shortentitles

Shorten a few titles
Merge branch 'dev' of https://github.com/saivann/bitcoin.org into opmodes
Merge branch 'opmodes' of https://github.com/instagibbs/bitcoin.org into opmodes
Added cross-references links to Transaction and Contracts sections
Improvements suggested by @saivann
Merge pull request #50 from harding/terms

Add cross-references
Apply a few suggested style improvements
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