Merge pull request #14 from mailjet/development

Merge development with master
update readme to v3.1.3

added new minor version and commit changelog.  includes various bug fixes as reported by users.
completed menu default value sentence

added value 101
description change

added newsletter key word
Update README.md
Merge development with master

Merge development with master
Merge remote-tracking branch 'origin/development'
Merge remote-tracking branch 'origin/development'
Merge remote-tracking branch 'origin/development'
Stop scripts from being output unnecessarily

I don't use widgets on my site at all but the ajax.js still gets output (and so loaded). Moving the enqueue to the widget output means the file gets output in the footer (which is better for speed) and stops it from being loaded when it's not needed.