This introduces a class for nicer wrapping and easier testing. Some
functions were changed to provide nicer APIs (no throwing around of
unescaped regexps) and to simplify things (hopefully).

The refactoring isn't completed yet, so this will break the subscription
system.

The goal is to move as much subscription related stuff to this class as
possible. Currently there is some code in lib/exe/indexer.php and maybe
elsewhere (common.php?). Additionally everything should be covered by
tests. A few tests are included here already.

* make use of $INPUT
* clean up coding style
* add phpdoc comments

makes it easier to access our do parameters

This fixes problems with setgid bits on the media directory

Seems like matching \b on unicode strings is unreliable across different
platforms (Debian). Using Unicode class lookahed/behinds seems to work
though.

This fixes a warning when setting $meta['relation']['firstimage']
using p_set_metadata.

In p_render() it is assumed that all renderers have a $doc variable

This includes a test for the minlen parameter for metadata keys