add new config params

- imagemagick_path
- quality_small
- quality_mini
update phpthumb to last available version (v2.0)

do this to get good support for imagemagick
add new options to setting class

- imagemagick_path
- quality_small
- quality_mini
refactor thumb and small method to support new phpthumb version

use quality config setting and imagemagick path, if given
use file_get_content instead of gd resource
use SourceImageToGD instead

use rotate without setting ra value
SourceImageToGD is unbelievable slow

so skip it and only use it for rotate case
Merge pull request #5 from Mischosch/phpthumb-update

Phpthumb update