Add -e flag to set sequence for escaping single quotes
Rationale: Some shells, like rc, don't support using backslash escapes
outside of a quoted string. In order for shsub to support such shells
without caveats, it is useful to specify an alternative escape sequence for
single quotes.
Ref:
https://doc.cat-v.org/plan_9/4th_edition/papers/rc
https://github.com/rakitzis/rc
Contributors
quexxon