Fix violations for Squiz.Commenting.DocCommentAlignment.SpaceBeforeTag

Conflicts:
	inc/parser/xhtml.php

This makes sure that the animal that is specified in the URL is actually
a subdirectory inside the farm and not somewhere else in the system.
This allows that the animals are organized in different subdirectories
for more complicated farm setups.

Now the animal can be specified in the animal environment variable.

* extracted most farm code into inc/farm.php
* by default farm.php is nowhere included
* added preload.php.dist as an example farm setup
* farm.php can be included in preload.php to activate farming