Use a consistent return_type for Count* primitives

[thehomebrewnerd]

In some counting primitives we are using a Double return type (like PartOfSpeechCount) while in others IntegerNullable is used as the return type (like NumUniqueSeparators).

Given that all of the counting primitives should be returning a whole number (or optionally null), IntegerNullable seems like a more appropriate return type to use than Double. We should investigate if there is a reason for using Double in some primitives, and, if possible, convert these to use an IntegerNullable return type.

Primitives to study:

• MedianWordLength
• PartOfSpeechCount
• PunctuationCount
• TitleWordCount
• TotalWordLength
• UpperCaseCount