Added text_color option.

Hi Greg!

I have tested the background_color option exception since I've also uses it for the new option text_color. It seems not working. See below codes:

        if ($options['text_color'] != array()) {
            if (count($options['text_color'])!=3) {
                throw new \RuntimeException('text_color should be an array of r, g and b');
            }

            $color = $options['text_color'];
            $this->builder->setTextColor($color[0], $color[1], $color[2]);
        }

        if ($options['background_color'] != array()) {
            if (count($options['background_color'])!=3) {
                throw new \RuntimeException('background_color should be an array of r, g and b');
            }
            $color = $options['background_color'];
            $this->builder->setBackgroundColor($color[0], $color[1], $color[2]);
        }


I tested the exception code by setting  the background_color: [255, 255]. I'm expecting that it would throw the exception but it does not. I noticed that it will never go to the exception message because it will never meet the conditions. So I fixed it with the codes below:

        if (isset($options['text_color'])) {
            if (count($options['text_color']) !== 3) {
                throw new \RuntimeException('text_color should be an array of r, g and b');
            }

            $color = $options['text_color'];
            $this->builder->setTextColor($color[0], $color[1], $color[2]);
        }

        if (isset($options['background_color'])) {
            if (count($options['background_color']) !== 3) {
                throw new \RuntimeException('background_color should be an array of r, g and b');
            }

            $color = $options['background_color'];
            $this->builder->setBackgroundColor($color[0], $color[1], $color[2]);
        }

And this works perfectly for me.

Hmm, I just noticed this after I commit the changes. 

If would be fine, it would be great if we can include these changes together with my pull request. 

Sorry for the mess.


Thanks!
Bert