Add document boundaries for unitizing measures

[chmeyer]

Originally reported on Google Code with ID 4

All processing multiple documents in unitizing measures. This requires a method for
defining the boundaries of the documents within the shared continuum of annotations.

TODO:
* create test case illustrating the issue,
* add method for setting the boundaries,
* Split the gaps at the beginning/end of a document.

Reported by chmeyer.de on 2014-07-25 13:43:22

[chmeyer]

Reported by chmeyer.de on 2014-07-25 13:46:19

• Labels added: Component-Agreement