Changed how potentially unset strings are handled in compose parsing.
Changed how potentially unset strings are handled in compose parsing.

This commit adds a simple nullableString type to handle compose command
line parsing cases where certain parameters are unspecified. String
pointers aren't a good fit for this because taking a pointer to a string
loop variable will take a pointer to the variable itself (basically the
same reason you don't want to fire off Goroutines using loop variables
without rebinding their values to function arguments).

Signed-off-by: Jacob Howard <f862f167b85d41b225785c70d70808bc7337c1fe@havoc.io>

havoc-io/mutagen,havoc-io/mutagen