When associative array, $options[0] is undefined

When $options contains the 'task' key in its associative array form, an exception will be thrown when trying to access $options[0]:

ErrorException [ 8 ]: Undefined offset: 0 ~ DOCROOT/vendor/kohana/minion/classes/Kohana/Minion/Task.php [ 105 ]

To replicate this independently of Minion's implementation, try running this:

php -r "echo ['task'=>'foo']['task'];"   // Will correctly print out "task"

php -r "echo ['task'=>'foo'][0];"  // Will throw PHP Notice:  Undefined offset: 0 in Command line code on line 1
_execute() requires the declaration of $params

As can be seen in line 281, the execute() method is calling _execute() with the validated $options obtained from CLI.

We must declare this argument in the abstract function so that overriding Task classes are able to receive this array.

```
// Finally, run the task
$this->{$this->_method}($options);
```

The implementation in Minion has always been that "$this->_options" represents the list of available parameters with their default values. In runtime, "$params" represents the validated input from the user, or simply the default values in lieu of any input.

I don't see a reason to introduce an API breaking change as part of this refactor.
Updating Minion task documentation
CLI baseclass
I/O Stream interfaces
CLI_Command execute() handles processing, invoked from index.php
Updates bundled Tasks
Updates Minion_Task to factory() and execute()
Adds Minion_CLI which implements all CLI interfaces for backwards compatibility
Uses long tags in task view
Adds support for CLImate formatted output
Removes deprecated file protection
Improves dependencies, decouples Task from other Kohana classes
Deprecates Fuel Team color(), use CLImate output for colors
Abstracting builders out of Command
Merge pull request #7 from cyrgit/3.4/feature/cli-interface-refactor

CLI interface refactor