Line issue trackers are conceptually a subclass of file issue
trackers: they're file issue trackers where issues arise from checking
each line independently. So make it an actual subclass.
Pylint pointed out the design smell: there was an abstract method that
wasn't always overridden in concrete child classes.
Detect Git merge artifacts. These are lines starting with "<<<<<<",
"|||||||" or ">>>>>>>" followed by a space, or containing just
"=======". For "=======", exempt Markdown files, because this can be
used to underline a title, as a compromise between false negatives and
false positives.
Exclude ".git" directories anywhere. This avoids spurious errors in git
checkouts that contain branch names that look like a file
check-files.py would check. Fix#1713
Exclude "mbed-os" anywhere and "examples" from the root. Switch to the
new mechanism to exclude "yotta/module". These are directories where
we store third-party files that do not need to match our preferences.
Exclude "cov-int" from the root. Fix#1691
