Move existing "regtest / testnet" texts to the new subsection and link to it
Move Bitcoin Core setup instructions in devel-examples
Add a consistent introduction for devel-(guide/ref/examples)
Fix autocrossref.rb to not add links inside {% highlight %} code blocks
* Remove the QR Code error corrections subsection.
* Remove the non-example Payment Protocol text from developer examples.
* Update reference links and autocrossrefs to reflect above deletions
* Fix CSS padding problems reported by @saivann
* Remove all HTML comments from autocrossref text to allow easy checking
for broken link definitions: find _site -name '*.html' | xargs grep '\]\['
* Add PNG versions of guide and example SVG icons. (optipng run)
