Add more colors.

New you can use all xterm-256 colors.
Add following colors : 
light_gray, dark_gray, light_red, light_green, light_yellow, light_blue, light_magenta and light_cyan

Add 2 color converter gray and rgb.

gray => 24 level of gray. you can use gray[0-255] of gray[0-100%]
rgb => 216 colors. you can use rgb[0-255|0-100%,0-255|0-100%,0-255|0-100%]

ex :
```php
<?php
$c = new Colors\Color();
echo $c('gray')->fg('gray[75%]');
echo $c('color')->fg('rgb[200,10,30%]');
```