Add ability to pass in an array of vals instead of as separate params

- Fixed so `del` now accepts an array of keys rather than just lots of
params (should work for other commands too)
- Added test cases for the `del` command, testing both multiple params
and one array param
- Updated `.gitignore` to include `node_modules`
Yeah I tried to take a more general approach to the problem to solve this issue for other commands that might take arrays. I certainly can do a wrapper style like that if you would prefer?