* Document the gem release process; add chandler

Releasing to rubygems.org is as simple as `rake release`, but there are
some additional steps around it to make sure our documentation is up to
date, which I've documented in `RELEASING.md`.

I've also added the `chandler` gem (my own creation) that automatically
updates the GitHub Releases whenever we run `rake release`. This ensures
that people can find our release notes easily.

This is the process I used to recently publish 4.0.0.alpha1.

* Clarify Chandler auth and provide example diff

The Rails incompatibilities with minitest have been fixed in the most
recent Rails releases. We therefore no longer need to pin to an old
version of minitest as a workaround.

* allow static_control to force a nil value

* add tests

* fix tests

…e specified. (#480)

…t helpers (#461)

* default form-inline class applied to parent content div on date select helpers

* Only engage inline form on date helpers when layout is set to horizontal, added a test

* error_summary: don't render surrounding div if there are errors

When there are no errors the div with for the error messages was still rendered, making it impossible to use css to style that surrounding div.

* Fix test case.

* Simplify conditional as suggested by reviewer.

#483)

* The `button`, `submit`, and `primary` helpers can now receive an additional option, `extra_class`.

…buttons. (#479)

* Rename div_class to make refactoring more obvious.

* Fix issue #476 for check_boxes.

* Fix issue #476 for radio buttons.

* Test for `:custom` option just once.

* Add wrapper_class for check boxes and radio buttons.

* error_summary: don't render surrounding div if there are errors

When there are no errors the div with for the error messages was still rendered, making it impossible to use css to style that surrounding div.

* Fix test case.

* Simplify conditional as suggested by reviewer.

* Rename div_class to make refactoring more obvious.

* Fix issue #476 for check_boxes.

* Fix issue #476 for radio buttons.

* Test for `:custom` option just once.

* Fix a Minitest deprecation warning.

* Preparing v4.0.0.