Allow setting rcfile path via flag

[lambdadog]

Also moves rcfile loading to worm.nim rather than events.nim, which feels more sensible.

I kept this simple and used std/parseopt because I didn't really want to pull in a dependency for command-line parsing since you weren't using one in wormc, but if using something more robust would be preferred I can do that instead (this is also why I only added a long opt and not a short one, since parseopt usage is quite verbose).

[codic12]

Looks good to me, thanks for all the PRs!