Adding new LOLCOMMITS_FORK (or --fork) option to fork the runner capturing

Use the LOLCOMMITS_FORK env variable or --fork argument in the lolcommits
command to fork the runner capturing process to a new thread.  Helps when the
capture is slow and you want to return to a usable terminal prompt right away.

Using fork, some plugins may prompt in your terminal after the initial capture.
README also updated to explain this.
DRY up steps a little
add passing test to verify forked mode doesnt break capture

In theory we should be testing to make sure it forks successfully, but
not sure how to do that...
Merge branch 'matthutchinson-allow-runner-forking'