This doesn't really do much except wrapping the functions into a
namespaced class. Autoloading takes care of loading the file.
It's now possible to call lib/exe/ajax.php multiple times in a test
request.

If a key is not set, a PHP Notice is triggered. While these are
currently suppressed, this is still a code smell.

This looks a bit better and is closer to the original, even though the
sizes are a bit weird now.

this got lost in a previous update

There was a bug that the empty string was considered to be invalid if
also a max or min value was defined for a config field of type
numericopt.

also dokuwiki and php are on https

added test coverage

While DokuWiki suppresses PHP Notices they are still a code smell and
should be fixed. This fixes some PHP Notices that occurred.

Some of these fixes could be refactored into nicer code once we move to
PHP 7 and get access to the `??` operator.

This makes sure the provided extension ID is a valid id before
initializing it in the extension manager.

No need to check those seperately. The correct order should be ensured
already.

Added green and red text color styles for geshi. Improves look of highlighted code for language diff. Fixes #900.