General Gen: PR feedback

Generalizes DocxGen to use an instance variable to set the templaterClass, allowing other adapters to be added with less duplication.  Originated here: https://github.com/contextmatters/docxtemplater/commit/d19aeaebbfef4d941e9a3c5c5085655038b6a07f#diff-9abb5f70f7742819ffc0f549f7aa32d1R22

thanks @edi9999 for the feedback / getting the last one merged in!