Adapt https://www.lua.org/work/diffs-lua-5.3.5-lua-5.3.6.html to
NodeMCU. Mostly a straight application, but some small tweaks were
required and, in lundump.c, some changes were elided and some additional
diff reduction applied, as we have heavily diverged from upstream.
- Lots of minor but nasty bugfixes to get all tests to run clean
- core lua and test suite fixes to allow luac -F to run cleanly against test suite
- next tranch to get LFS working
- luac.cross -a options plus fixes from feedback
- UART fixes and lua.c merge
- commit of wip prior to rebaselining against current dev
- more tweaks