Make travis build the 2.0 branch

This branch will be the target of pull requests, so I'd like to have CI
running on it as well.
Remove unnecessary autoload call from PasswordStrategies module.
Bump version to 2.0 alpha

This will allow me to test some apps from GitHub as we developer 2.0 and easily
disambiguate the installed version.
Add a setting to disable all routes

This setting allows clearance routes to be completely customized. Users who
customize the routes to this level may have to edit the views and mailers as
there are references to routes there.
Update spec style

Use updated spec style.

* Eliminate before blocks
* Eliminate let statements
* Use expect syntax
* Use method describes rather than contexts
Add generator to copy default routes to the app

The generator configures clearance to turn off its internal routes and
then copies the default routes to the host application's routes file
where they can be customized to the developer's content.
Remove support for Rails 3.2

The maintenance policy for rails is to support the last two release
series'. This would be 4.1.x and 4.0.x at this point.

Clearance 2.0 drops support for 3.2
Update views to use 1.9 hash syntax
Remove all previous deprecated code
Remove allow_sign_up configuration option

This options is removed in the interest of limiting the number of ways to
accomplish the same or similar tasks. If you wish to customize clearance
routes, run the `clearance:routes` generator to turn off the internal
routes and copy them to the host application for customization.