* DEV: Switch our fast_xor gem for xorcist
We use the `xor` function as part of password hashing and we want to use
a faster version than the native ruby xor'ing feature so we use a gem
for this.
fast_xor has been abandoned, and xorcist fixed our initial holdup for
switching in https://github.com/fny/xorcist/issues/4
xorcist also has jruby support so we can remove our jruby fallback
logic.
* Move using statement inside of class
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
