Fix: Adding per-environment rule configs to docs and doc validation (Fixes #918)

This change adds info to the docs about rules that have been overridden in [the environments.json config](conf/environments.json):

[Rules README.md](docs/rules/README.md):
> * [handle-callback-err](handle-callback-err.md) - enforces error handling in callbacks (off by default)
> * [handle-callback-err](handle-callback-err.md) - enforces error handling in callbacks (off by default) **(on by default in the node environment)**

It also adds validation to [Makefile.js](Makefile.js) to verify that the environment settings are listed in the docs. If a rule has specifically been set for an environment, its setting must be in the docs, whether it was turned on or off. The idea is that a rule will only be set for an environment if it differs from the default.

This is meant to address #918.