[bug] Eliminated an implementation flaw
[documentation] documentation update

The documentation now reflects the latestest updates and the metadata of
the plugin (the things that appear on the WPs plugin page) have been
updated.
[doc] Added 'known issues' file
[feature] Added Vagrant support

By means of Vagrant the entire development environment can be installed
using only a oneliner: 'vagrant up'.
The required files reside in the 'vagrant' directory.
The documentation has been updates accordingly.
[bug] Git refused the vagrant/src dir, since it was empty
[bug] Minor bugs regarding vagrant fixed
[bug] Fixed link insertion flaw

There was a flaw in the subroutine that inserts a hyperlink into the
WYSIWYG-editor. It has been corrected now.
Merge branch 'dev'