[*] Class Tools: enhance fd method

Add the posibilities to set an error, warning, info or assert.

Usage:
Tools::fd('test');
		Tools::fd('test', 'debug');
		Tools::fd('test', 'info');
		Tools::fd('test', 'warn');
		Tools::fd('test', 'error');
		Tools::fd('test', 'assert');
Merge pull request #229 from PrestaEdit/patch-18

[*] Class Tools: enhance fd method