Parallelize encryption to improve performance

[burke]

@Shopify/locutus

Turns out encryption is pretty slow.

Time to decrypt test file fetched from https://edg.epa.gov/data.json and encrypted with a random key:

On my macbook:

• Go 1.4, GOMAXPROCS=1, master branch: 7.8s
• Go 1.5, GOMAXPROCS=1, master branch: 5.8s
• Go 1.5, GOMAXPROCS=1, this branch: 6.9s
• Go 1.5, GOMAXPROCS=8, this branch: 1.9s

On production infrastructure (first is Go 1.4, 1 proc, master; second is Go 1.5, 32 procs, optimize branch):

burke@borg3.ash:~ $ ./test_deployed
7.371902681s
burke@borg3.ash:~ $ ./test_go_1.5_optimize_branch
794.795795ms

[burke]

Damn, turns out the profile result I was originally looking at that motivated this was from when we were still invoking ejson as bundle exec ejson. Our ejson files aren't actually big enough that this really pays off; most of the cost was from loading bundler and ruby. This'll only save us like 50-100ms.

[csfrancis]

Oh that's too bad. It's still pretty cool though.

:+1: