Use simditor as dependency

Make sure always get latest version to avoid issues.
Allow override on toolbar items through attribute

Use can add "toolbar" attribute in directive to override toolbar items.
e.g.   
<div simditor name="content" ng-model="content" toolbar="['title', 'bold', 'italic', 'underline', 'strikethrough', '|', 'ol', 'ul', 'blockquote', 'table']" form-required="true"></div>
Support ngRequired as part of angular form submition

Allow user to add attribute "ng-required" as same as other standard angular form elements.
it will set the $error.required error flag as standard.

The below error message will show when form validated.
<span ng-show="xxxForm.content.$error.required && validated" class="error">XXX不能为空</span>
should listen to valuechanged event on simditor

Looks like I need to merge with latest code.
merge realdah