Allow users to choose the name strategy of fields

[kinow]

Closes #78 related to #75

In https://github.com/kinow/protobuf-uml-diagram/issues/10 we changed how names of fields were chosen, as there could be fields with the same name, but that meant/were different things. Instead, we started using the field full name (i.e. Airplace.wing, Chicken.wing instead of just wing).

In this pull request we allow users to change that behavior if they are sure that will not cause any issues, or if they prefer for aesthetics.

Thanks to @danjohles for reporting it.

-Bruno

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[kinow]

Just pending unit tests, changelog entry, docs. Tested with the sample protobuf from the docs.

protobuf_uml_diagram.py --proto test_data/issue_10.proto --output /tmp

#or 

protobuf_uml_diagram.py --proto test_data/issue_10.proto --output /tmp --full_names=true

$ protobuf_uml_diagram.py --proto test_data/issue_10.proto --output /tmp --full_names=False

The difference is the new parameter --full_names=true|True|False|false|<default=true>.