v1.0.1: Check code with megacheck

Fix everything we can without losing Go 1.5 compatibility. Add
megacheck, locked at 2017.1 release, and enabled for any version of Go
except Go 1.5, to the Travis scripts to check every PR.

Fixes #662.

Original version

Merge pull request #481 from cbandy/array-error

Fix panic when parsing malformed array input