Add dev docs generation to Jenkins:

Fixes: RIPD-1521

Switch to pure doxygen HTML for developer docs. Remove docca/boostbook
system. Convert consensus document to markdown. Add existing markdown
files to doxygen input set. Fix some image paths and scale images for
use with MD links. Rename/cleanup some files for consistency.
Add pipeline logic for windows slaves. Add ninja and parallel test run
option. Add make doc target build in build-and-test.sh. Cleanup README
files. Add nounity windows build. Add link to jenkins summary table.
Add rippled_classic build (win). Improve formatting of summary table.

src/ripple/README.md

@@ -1,4 +1,4 @@
-### Newest Style
+# Ripple Source Guidelines
 
 Each folder contains a single module following the newest style:
 

src/ripple/overlay/TODO.md

@@ -1 +0,0 @@
-# Overlay