Added supprt for selecting wordpress users

I really didn't do much here.
Merge pull request #402 from UsabilityDynamics/master

Class name lookup update and added composer.json
New color for new admin theme
Version 4.3.7
No longer uses `get_called_class` function. #384
Small optimization for field class
Version 4.3.8
Merge remote-tracking branch 'upstream/master'
Update support for user to use new RWMB_Base Class

update new field after a long overdue merge with the master repo
Merge pull request #409 from michaelhume/master

Add support for 'Users' Field
Added "category" in better include demo
Merge pull request #412 from jorpan/master

Added "category" in better include demo
typo
version
Merge pull request #414 from corvannoorloos/master

fix typo and update json version number
Update select2.css
Merge pull request #419 from krishna19/patch-1

fix height of select_advanced type
Fix bug in "text_list" field type

Fixed bug in "text_list" field type.
Merge pull request #421 from tonetlds/patch-1

Fix bug in "text_list" field type
Update image.php

Theme Check Error. Fix for Non-printable characters were found in the image.php file.