Typos primarily works off of identifiers and words. We have built-in
support to detect constructs that span identifiers that should not be
spell checked, like UUIDs, emails, domains, etc. This opens it up for
for user-defined identifier-spanning constructs using regexes via
`extend-ignore-re`.
This works differently than any of the previous ways of ignoring thing
because the regexes require extra parse passes. Under the assumption
that (1) actual typos are rare and (2) number of files relying on
`extend-ignore-re` are rare, we only do these extra parse passes when a
typo is found, causing almost no performance hit in the expected case.
While this could be used for more generic types of ignores, it isn't the
most maintainable because it is separate from the source files in
question. Ideally, we'd implement document settings / directives for
these cases (#316).
