Log Message:
Update to 0.42. From the git log:

- mkdocs: enforce sufficiently new version, and use mkdocs-exclude.
- cookbook/container: example of building+running docker containers.
- cookbook/container: add missing PS1 to sh example
- Merge pull request #25 from ejona86/missing-ps1
- cookbook/container: remove unexplained "exec >&2" lines.
- cookbook/container: skip on missing cpio and missing kvm kernel image.
- cookbook/container: some minor clarifications.
- cookbook/container: minor proofreading
- Merge pull request #26 from martinmosegaard/proof-cook-container
- Better handling if parent closes REDO_CHEATFDS or MAKEFLAGS fds.
- docs/cookbook/container: don't delete *.out and *.code during build.
- mkdocs: include additional hljs languages.
- Fix builder: Reinstate stderr instead of opening /dev/tty
- Merge pull request #27 from spacefrogg/fix-tty
- cookbook/container/kvm: better handling of \r\n line endings.
- mkdocs: exclude more generated files from cookbook/container.
- Merge remote-tracking branch 'origin/master'
- mkdocs: exclude more generated file types.
- Experimental new redoconf C/C++ build/autoconfiguration system.
- redoconf: avoid sed -E in _objlist().
- redoconf: clock_gettime() detection needs to depend on -lrt.
- redoconf: better handling of required vs optional detectors.
- redoconf: posix.rc: fix abort when timespec is not available.
- Fix some build problems on MacOS X.
- minimal/do: remove dependency on 'seq' command.
- Precompiled headers: supply "-x c-header" or "-x \ 
c++-header" if available.
- docs/cookbook/c/allconfig.do: avoid need for '&' backgrounding.
- mkdocs: don't bother to include cookbook/c/out.*/ dirs.
- redoconf: move -Wl,-rpath flags to shlib.rc and add -Wl,-z,origin.
- minimal/do: remove dependency on 'seq' command.
- Certain redo post-build failures would still mark a target as built.
- Overridden files were accidentally getting reclassified as static.
- If redo searched all the way up to /default.do, it would run ./default.do instead.
- Explicitly reject target/source filenames with newlines in them.
- redo-ifchange regression: if REDO_LOG is not set, assume it's 1.
- builder.py: atomically replace the log for a given target.
- Merge branch 'master' into redoconf
- redoconf: assorted minor fixes.
- redoconf: a stub rc_include() now sources ./redoconf.rc automatically.
- Merge branch 'redoconf'
- logs.py: don't print (unchanged) lines with --no-log unless DEBUG.
- Change -x/-v to only affect top-level targets by default, not recursively.
- redo-log: sometimes print a (resumed) line after ending a level of recursion.
- Minor clarifications to redo install instructions.
- shelltest.od: warning 84 (W84) triggered on *all* shells, not just posh.
- Work around ancient shells where >$3 does not implicitly quote $3.
- docs/cookbook/container: update docker image builder.
- docs/cookbook/redoconf-simple: a simple redoconf C++ project.
- builder.py: create temp log file in the same directory as the final one.
- Unset CDPATH if it is set.
- redo-log: "(resumed)" lines didn't print as often as they should.
- Fix minor pylint warnings.
- redoconf/configure.sh: use "cmp -s" to silence output.
- cookbook/container/default.sha256.do: use explicit close_fds=False.
- Fix more problems with "/usr/bin/env python" picking python3.
- Merge remote-tracking branch 'origin/experimental/dockrepo'
- Oops, redo/whichpython.do would fail if python2.7 didn't exist.
- Disable docker container test from toplevel 'redo test'
- t/103-unicode: workaround unicode normalization on newer macOS.
- t/shelltest.od: Add a new preliminary test for IFS= behaviour.