Do not require parens for `defeffect`

I got curious and wanted to play around and was able to make `defeffect` work without requiring parens. No worries if you want to close (or re-implement) but I think it would be nice for those who follow it to be able to stay consistent. Also just FYI, there is a bunch of trailing whitespace `lib/efx.ex` which makes diffing a pain when you have a strip-whitespace enabled editor. Fixes #1