Docx reader: Fix bug in character styles.

Style handling has been cleaned up, but introduced a bug here. There
wasn't previously a test to catch it.
Docx reader: Test for character styles.
Docx reader: Remove unnecessary plural functions

functions like runElemsToInlines and parPartsToInlines are just defined
in terms of concatting and mapping their singular
version (e.g. `runElemToInlines`). Having two functions with almost
identical names makes it easier to introduce errors. It's easy enough to
just concat and map inline, and it makes it clearer what is going on in
the code.
Merge pull request #1540 from jkr/charStyles

Char styles