* Amend `.codecov.yml` to disable coverage reporting of test sources
and explicitly set most parameters
* Increase codecov upload retry time to 210s (from 35s)
* Upgrade gcovr adding support for more coverage formats (lcov, clover, jacoco)
* Upgrade github actions in coverage workflow
* Explicitly disable codecov plugins (also removing `gcov` coverage, which is not
correctly handled by codecov https://github.com/codecov/feedback/issues/334)
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.
