* caca_dithering_bitmap can load palette from gd resource
* Remove caca_set_dither_palette_gd function
* Adapt sample program "dithering.php"

* Modify php bloc headers in samples programs
* Add list of import/export formats in examples/drivers.php

given gd resource.

render it with caca caca_dither_bitmap_gd)
* Add a function to fetch a buffer of gd pixels in php_caca.c

* Add php binding for "caca_create_dither"
* Add new sample program "dithering.php"