Feature: Enable chamber by default in overcommit
Chore: Update gitignore to latest version
Chore: Update jscsrc to latest version
Refactor: Update rubocop config to split rails from core

The Rails-specific Rubocop config needs to be split out from the core rubocop
stuff.  The main reason for this is that we don't want to have to _disable_ the
Rails checks in every non-Rails gem that we have.

Instead, we just create a `.rubocop_core.yml` file which is always included and
contains the bulk of our configuration.

Then, each project would have a `.rubocop.yml` file which would include
`.rubocop_core.yml` at the top, and then modify any other settings it would like
below that.

We also split out our Rails-specific stuff into `.rubocop_rails.yml` which is
also included in the main `.rubocop.yml` file.

In this way, we can mass-update `.rubocop_core.yml` and `.rubocop_rails.yml`
without affecting the project-specific settings.
Feature: Add gemspec template