Add WYMeditor.editor.$body function.
Document WYMeditor.editor.$body.
Add WYMeditor.editor.body
Document WYMeditor.editor.body.
Make WYMeditor.editor.$body use WYMeditor.editor.body .
Implement WYMeditor.editor.body & WYMeditor.editor.$body in all the things.
Merge pull request #525 from wymeditor/issue_525

Closes #525. Add a WYMeditor.editor.$body function
CHANGELOG for `WYMeditor.editor.body` & `..$body`.
Merge branch 'master' into issue_587