Feature request: ability to add lineSpacing to the Docx API

[mikeappell]

First of all, thank you for an amazing, easy-to-use module with an extraordinarily understandable API.

I was wondering what the difficulty in adding a lineSpacing option for createP() would be – or, alternately/additionally, being able to set a default for the whole document.

There's an existing Pull Request (#198) which attempts to add this function to the paragraph API, and the code seems very straightforward. It fails the Travis tests, but that may simply be because the PR was from 2017 and there have been significant changes around the affected files since then. I'd be happy to re-create the PR using the current state of the codebase if you prefer.

I need this ability for my current project, so otherwise I'll end up having to fork this repo and add the commit from the PR myself.

Thanks!