WPDb term operations updated

Another update to the WPDb module for term operations.

Term operations

I've refactored the term related methods of the WPDb module part of the wp-browser add-on for Codeception refactoring many and testing any I've modified.
The details are in the README file or, in a code-friendly way, in the change log file.

Next

The changes pave the way to a powerful post insertion API that I've outlined in an earlier post and gets me closer to making this code possible in an acceptance or functional test:

$terms = ['taxonomy_one' => ['term_one','term_two']];
$I->havePostInDatabase(['terms'=> $terms]);