[UPDATE] Support for the new Vagrant plugin API - 1.2.

Support for <1.2 is now deprecated and lives on the plugin_api_1.1
branch.

Squashed commit of the following:

commit 27c103ad2fa2054059da6d24c17fbfc7c78add6f
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Mon May 27 13:58:42 2013 +1000

    [WIP] Finalise support for plugin API 1.2

    * now supports auto_unmount.
    * cleanly handles directories and filenames.
    * a minimum of configuration options

commit c3dab49ae36d6c08a2965be63fad4bb3a3b272c7
Merge: 72c44e6 af1d771
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Mon May 27 09:25:45 2013 +1000

    Merge branch 'plugin_api_1.2' of github.com:Learnosity/vagrant-sparseimage into plugin_api_1.2

commit 72c44e6ed0a39887d3c33f8e5fd02c0827c828fa
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Mon May 27 09:24:57 2013 +1000

    [WIP] Handle config differently in example vagrantfile.

commit af1d77115ccb6a77abe90bae5e554bb042182f37
Author: Alan Garfield <alan.garfield@learnosity.com>
Date:   Sat May 25 09:49:06 2013 +1000

    [WIP] Fixed a few spelling mistakes

    The "destroy" doesn't remove the image file.

    Also how do we deal with required options not being set now?

commit 06c1a2a98231d553a79de2d95ce5cb4d7a75ec6b
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 18:12:51 2013 +1000

    [UPDATE] Fiddling with metaclass to maintain sparse images state..

commit 293852e41fd568181522629a607d870da0a637af
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 18:03:06 2013 +1000

    [FIX] Uncomment the halt and destroy hooks.

commit 6b389d27ebf7b58b49221e09298cb1e48dc95b5c
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 18:02:11 2013 +1000

    [TWEAK] Add .gitignore.

commit 7862bd49b632e41fbaf2c102fd447fdf5feedc8a
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 18:01:46 2013 +1000

    [NEW] Add example box.

commit cfc19df885f80e1c946eb0aec363271934149fd3
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 17:58:08 2013 +1000

    [WIP] Reduce code footprint, move to single-file plugin. Still does not
    work - config state not getting passed around consistently.

commit d7d992a5bf133d31776472fd1b5e5fbcae2127d9
Author: Daniel Bryan <danbryan@gmail.com>
Date:   Fri May 24 14:36:58 2013 +1000

    [WIP] - Upgrading to support the Vagrant 1.2 API.

    Matches the examples for 1.2, but still does not work. The
    config block for the images doesn't seem to be evaluated.