From upstream
Merge branch 'develop' of https://github.com/PHPOffice/PHPWord.git into develop
Merge branch 'develop' of https://github.com/PHPOffice/PHPWord.git into develop
Merge branch 'develop' of https://github.com/PHPOffice/PHPWord.git into develop
Merge branch 'develop' of https://github.com/PHPOffice/PHPWord.git into develop
Added Field Element
Travis build error fix
Update changelog, docs, and unit tests for new `Field` element #251