Add support for columns and page margins

[halleysfifthinc]

I followed the ECMA-376 spec for both columns (definitions/descriptions in §17.6.3 and
17.6.4), and margins (§17.6.11).

Fixes #30.

[halleysfifthinc]

Friendly bump!

[jkrumbiegel]

Thanks for the PR! I'm on vacation currently so will need a bit until I can get to it

[jkrumbiegel]

Thanks for the PR, I have some smaller comments but in general this already looks quite good :)

[jkrumbiegel]

I fixed a small bug with the kwargs but it looks like the custom column widths don't yet work. If I repeat the text in the test case it looks like this:

[jkrumbiegel]

It still doesn't look correct, now there's one smaller column which is progress, but the text doesn't go into the other one, suggesting there's something wrong with the generated xml

[halleysfifthinc]

Interesting! It seems that LibreOffice and Microsoft Word handle that differently, because the same test in LibreOffice wraps as expected.

[jkrumbiegel]

Hm yeah that can happen with different rendering engines. I would create a file with the desired column layout directly in Word, unzip the docx file and then compare the XML inside with what we generate here. If you don't have access to Word, I can also make such a file

[halleysfifthinc]

I have Word; I'll finish this up sometime this week.

[jkrumbiegel]

Looks good now on my end!