Add functionality to support dokuwiki title [[y:/path/fo/file|Title]] and fileservers in the mapping.php file

The dokuwiki title syntax is now supported. This fixes issue #2.
It is now also possible to write a fileserver for each drive letter in mapping.php. This takes then precedence over the setting in `conf['fileserver']`. However the setting is retained to provide an option for an "default" fileserver and to ensure backwards compatibility.

Internally it was necessary to remove the copied `windowssharelink` function and move back to the original function in `inc/parser/xhtml.php`. This had the consequence that the class for a (non-)existing link has to be fixed afterwards.
Also having possibly two settings on each line in mappings.php made it impossible to use `conToHash` directly so that each line has to be sorted manually.