Feature request: PHPdoc parser to populate command help

I've implemented the feature request I named in #64 where the phpdoc-block was parsed for information to populate descriptions for arguments and options. It also improves the command description parsing by putting all but the first line in the help section.

In other words, it turns
```php
/**
 * Calculate the fibonacci sequence between two numbers.
 *
 * Graphic output will look like
 *     +----+---+-------------+
 *     |    |   |             |
 *     |    |-+-|             |
 *     |----+-+-+             |
 *     |        |             |
 *     |        |             |
 *     |        |             |
 *     +--------+-------------+
 *
 * @param int $start Number to start from
 * @param $steps int Number of steps to perform
 * @param array $opts
 * @option $graphic Display the sequence graphically using cube
 *                  representation
 */
public function fibonacci($start, $steps, $opts = ['graphic' => false])
{
}
```
into
```
$ ./robo fibonacci --help
Usage:
 fibonacci [--graphic] start steps

Arguments:
 start                 Number to start from
 steps                 Number of steps to perform

Options:
 --graphic             Display the sequence graphically using cube representation

Help:
 Graphic output will look like
     +----+---+-------------+
     |    |   |             |
     |    |-+-|             |
     |----+-+-+             |
     |        |             |
     |        |             |
     |        |             |
     +--------+-------------+
```