Update to state that subrepo is used in production environments.

Fixes ingydotnet#621

A number of places had incorrect quoting. Fixing this found that
the paths for some tests were incorrect in the status tests.

git 2.30 added a check to ensure the permissions in the .git
folder were "reasonable". When running the test in docker the
user is different than the host machine and it was throwing a
different error than expected when doing a git subrepo status
inside the .git directory. Add a configuration option to ignore
the permission mismatch during testing.

Git 2.33 and later ask the user what strategy to use when pulling
This broke the pull-force test as git returned an error including
how to set the setting. Added the default setting to the command
to prevent this issue during tests.

Add newer git versions to the docker file

Allows for testing a greater set of git and bash configurations

- Convert testing to use docker with updated git versions
- Fix numerous places where quoting was incorrect causing path name collisions
- Fix pull-force test to deal with git not defaulting to merges on pulls after 2.33
- Fix issue where docker tests didn't work with git 2.30 or higher because of
  increased permission scrutiny.
- Update readme to say this tools is in production environments
- Update readme to use internet archive for old articles about subrepo no longer
  available on their original source