incoming: use named groups in start-of-the-string regex

linters: jshint config

checker: configurable allowed exit codes for linters

linters: luacheck config

linters: yamllint config

linters: flake8 config

checker: don't hardcode linter config, load it from files

checker: go back to using hg files with -I and -X Because -X is a bit simpler than a fileset that also excludes some files (to code and just visually). Also rename property to "include" for clarity.

checker: try and catch exceptions from execute() and somewhat finish the job Exceptions coming from execute() are programming errors in checker.py, but jobs still need to tell that they are finished (and failed) to be processed by incoming.py.

checker: make run_ignore_1() a bit more flexible by adding codes argument