Add deployment tasks for use with Capistrano

This script, when required into a user's deployment script, provides
several useful tasks for deploying an application with Thinking Sphinx.
These tasks are:

 * `cap thinking_sphinx:configure`: Generate the .conf file
 * `cap thinking_sphinx:index`: Build Sphinx indexes
 * `...:rebuild`: Stop, rebuild indexes, and start the search daemon
 * `...:stop`: Stop the search daemon
 * `...:start`: Start the search daemon
 * `...:restart`: Restart the search daemon
 * `...:shared_sphinx_folder`: Create a shared folder for indexes
 * `...:symlink_indexes`: Symlink indexes into the latest release

Additionally, the `thinking_sphinx/capistrano` script will setup some
logical flow for deployments. After a cold deploy, indexes will be built
for the user and the search daemon will start up. During a
`cap deploy:setup`, a shared folder will be created to store Sphinx
indexes. Finally, after each release is finalized, symlinks to the
shared indexes will be created.

This commit closes #447.

Signed-off-by: David Celis <me@davidcel.is>