tools: introduce `make mdlint` command and tools
Summary
I'm trying to put this PR as a replacement for https://github.com/nodejs/node/pull/11610 and https://github.com/nodejs/node/pull/8551.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
tools, doc