Otherwise if caret is in the middle of reference, standard dummy identifier
will break docstring format and existing references used for completion
will be lost.
For example previously line "param (int) : foo" became
"paraIntellijIdeaRulezzz m (int) : foo" and Google code style docstring
parser wasn't able to reparse it and extract necessary parameter
reference.
To use alternative dummy identifier I moved populating completion
variants from DocString*Reference classes to PyDocstringCompletionContributor.
