This goes to a separate file because that makes option parsing easier
and allows profiling both at the same time.
The "normal" profile now contains only the profile data of the actual
run, which is much more useful - you can now profile a function by
running
fish -C 'source /path/to/thing' --profile /tmp/thefunction.prof -c 'thefunction'
and won't need to filter out extraneous information.
This reads any additional positional arguments given to `fish -c` into
$argv.
We don't handle the first argument specially (as `$0`) as that's confusing and
doesn't seem very useful.
Fixes#2314.
