Feat/custom scope opts

[nikcorg]

this is the meat of the change made by @jgwmaxwell to this fork. let's keep our local master up to date with upstream and rebase this PR (without actually merging) to keep updates manageable.

DON'T MERGE THIS PR!

To update our fork, follow these steps:

1. clone this repo
2. add upstream as remote
3. fetch upstream
4. reset this repo's master to the upstream master
5. force push the updated master
6. rebase this PR onto the updated master

or in commands

git clone [email protected]:musicglue/pow.git && cd pow && \
git remote add upstream https://github.com/danschultzer/pow.git && \
git fetch --all && git reset --hard upstream/master && git push --force origin master && \
git checkout feat/custom-scope-opts && git rebase master && git push --force origin feat/custom-scope-opts