Add phpdocs for Redis commands in Predis\ClientInterface.

This commit addresses a long-standing feature request posted in #89.
Added a .gitattributes file
Added Predis\ClientContextInterface.

This interface replaces Predis\ExecutableContextInterface and it is
used by client-side contexts such as pipelines or transactions.
Added @method tags to phpdoc header of Predis\ClientContextInterface.
Include docs
Merge pull request #194 from GrahamCampbell/gitstuff

Added a .gitattributes file
Makes it easier to use a custom parameters class.

Simply overriding one method of the standard connection factory class,
used internally by Predis, allows developers to use their own custom
connection parameters classes through the whole library.

For example, in order to support Heroku-style URIs one can do:

  class HerokuParameters extends Predis\Connection\Parameters
  {
    protected function filter(array $parameters)
    {
      if (
        isset($parameters['scheme']) &&
        $parameters['scheme'] === 'redis'
      ) {
        $parameters['scheme'] = 'tcp';
      }

      if (isset($parameters['pass'])) {
        $parameters['password'] = $parameters['pass'];
      }

      unset($parameters['user'], $parameters['pass']);

      return $parameters;
    }
  }

  class ConnectionFactory extends Predis\Connection\Factory
  {
    protected function createParameters($parameters)
    {
      return HerokuParameters::create($parameters);
    }
  }

  $client = new Predis\Client($_ENV['REDISCLOUD_URL'], [
    'connections' => new ConnectionFactory()
  ]);

This idea comes in response to #196, but since we do not want to bake
support for SaaS-specific URIs in Predis this is the best compromise
we can offer leave developers free to implement their own logic for
handling these kind of URIs with the additional benefit of having it
available through the whole library (think of cluster or replication
where you have multiple nodes, thus multiple instances of connection
parameters to create).
Merge branch 'v1.0/custom-parameters'
Update README.

[ci skip]
Predis\PubSub\DispatcherLoop should take a PubSub consumer instance.
Miscellaneous fixes for "use" directives.
Merge branch 'v1.0/phpdocs'
Fix code smells.
[phpdoc] Various phpdoc fixes.
The \Iterator interface returns void for next().
Comply with PSR-2 on intentional fall-through in non-empty case.
[phpdoc] Fix undefined namespaces.
[phpdoc] Fix undefined classes.
More random fixes after inspection.
Remove useless argument from method signatures in WebdisConnection.