Added support for table styles while preserving existing default behavior

Hi Mike,

See my comments on this commit on my fork for more details. Headline is I needed support for specifying the look and feel on many tables across my documents by providing table styles. This change accomplishes that, although in practice would generally require additional table styles to be added to styles.xml. I'm noodling how to add new styles without having to override the entire templates directory, but that will need to wait for another weekend :)

In the meantime, I'm inclined to believe this patch adds new capability while well preserving legacy behaviors.

Please do let me know what you think if you don't find it suitable, will find a way to make it fit into the bigger picture :)

Also, btw, I sent you an email directly yesterday, not sure if you got it, but I might be willing to take over maintainer duties from you on this project.

--Best,
Steve

## Commit comments
* Allow tblStyle to be specified along with tblLook (which elements of
tblStyle to apply in this case). Defaults produce same behavior as
prior version.
* Miscellaneous corrections to typos in comments and extra blank lines.