feature: Shape.alternative_text

[fsolleza]

Hi,

I added a little bit of code and two tests associated with that code so that users can add alt text to inline shapes.

The API is consistent with InlineShape.height and InlineShape.width without modifying the InlineShape initializer or changing the add_picture method. This change was based off comments in #227.

Users can add alt text as follows:

from docx import Document

doc = Document(path)
pic = doc.add_picture(picture_path, cx, cy)
pic.alt_text = "some alt text"

I'm happy to take any input and make changes where you deem necessary.

Thanks!

[scanny]

Hi @fsolleza: reopening this one (with slightly changed name) to serve as a feature request for Shape.alternative_text.

[neuhausr]

Hi, this is something I would also find useful (alt-text is necessary for document accessibility). Do you know if something else needs to be done to merge this change? Thanks!

[jeffreinhart]

Also interested in seeing this merged. Thanks!

[yosukefk]

Just clone repo, fetch this pr, and it worked as advertized. So it would be nice if this got merged to master.