Remove the salt from the DB migration

The salt column is only needed for SHA1 and MD5 strategies, which  are
not the default. The README contains instructions for adding the salt
back before switching to those strategies.
Add Appraisal install line to CONTRIBUTING.md

* Setting up Appraisal is necessary to run the test suite.
Apply style guidelines

* Use single quotes unless interpolating.
* Do not align tokens.
* Add a newline between lines of code and blocks.
* Alphabetize methods and lists of attributes.

Additional refactoring:

* Refactor new_indexes to more appropriately use a Hash.
* Refactor collections to use Symbol#to_proc to shorten lines.
* Use consistent naming patterns (existing_*, new_*).
* Remove `each` naming convention on enumerators.
* Remove now unnecessary GOALS file.
Overhaul README.md

Intention is to better communicate the API.
[#206] Improve data integrity

By default, we want email, encrypted_password, and remember_token to
enforce a NOT NULL constraint.
[#204] Remove flash message from users#create

* Flash message is redundant to validation error displayed by
  libraries such as dynamic_form, simple_form, or formtastic.
* We are not bundling one of the form libraries with Clearance
  in order to leave that decision to the developer.
Upgrade dependencies

* Support Rails 3.0.15, 3.1.6, 3.2.6.
* Apply style guidelines to test suite.
* Be more strict about development dependencies.
Clearance cannot be added to an existing app

Since the generated migration adds non-NULL requirements to columns, and
since we never add Clearance to existing apps, we cannot trivially test
the nuances involved in that situation. For now, we do not support this.
Re-arrange the gemspec to be in a more canonical order
Require Ruby 1.9.2 or anything greater
Bump to 1.0.0.rc1
Link to the real contribution guidelines.
Correct NEWS and README

* You can use Clearance after you've created a Rails app or users
  table. If you have users already, you'll need to edit the default
  migration that Clearance generates.
* We are testing against latest Rails 3.0.x, 3.1.x, and 3.2.x.
Use a released version of addressable in Gemfile.lock

addressable 2.3.1, the version to which the Gemfile was previously
locked, has been yanked:

https://rubygems.org/gems/addressable/versions
Relax bundler dependency so bundle install will work with more recent bundler updates
Appraisal droppings
Rescue BCrypt Invalid Hash only in migration strategy
Add password variable set in the SHA1toBCrypt migration strategy
Improve README

* Generalize versions of Rails/Ruby we test against.
* Add `bundle` line.
* Order main API walkthrough by importance and group authorization.
* Use Ruby 1.9 hash syntax.
* Get closer to 80 character limit on lines with links.
* Use Ruby . or # syntax to evoke class or instance method.
* Add Code Climate badge.
Update LICENSE copyright years

* Update LICENSE to agree with README.md copyright years