add taxonomy_multi_select field to the readme

see #51 and see #14
Merge branch 'master' of github.com:Automattic/custom-metadata
Merge branch 'master' of git://github.com/Schreiber-und-Freunde/custom-metadata into Schreiber-und-Freunde-master
minor fixes to pull request #81

* coding standards adjustments
* remove some unused code

fixes #81, fixes #82
props PhilippSchreiber
Adjustments to the README based on features added
Merge pull request #1 from Automattic/master

Pull changes from Automattic repository