Pptx reader added

[aantich]

• Read pptx format
• Parse "smart art" diagrams
• smart list detection

[jgm]

These .gitignore changes are specific to your setup and probably shouldn't be included in the PR.

[jgm]

ditto

[jgm]

Thanks for the PR! I'm testing it locally, and here are two things I noticed.

Slide titles

% pandoc -f markdown -t pptx | pandoc -f pptx -t markdown
# Slide one

content

# Slide two

content two
^D
## Slide 1

Slide one

content

## Slide 2

Slide two

content two

Pandoc normally uses headings with the slide title, but these get replaced by the pptx reader with "Slide 1", "Slide 2" etc. Can this be fixed?

Missing p:sldIdList

When I generate pandoc's default reference.pptx and try to read it with this reader, I get:

Failed to parse PPTX: Missing p:sldIdLst

But the file opens just fine in PowerPoint; I think it is valid, hence that p:sldIdLst may be optional? Can we handle the case where it is missing?

[aantich]

thank you, on it

[jgm]

In addition, the new format should be added to MANUAL.txt ; see the list under --readers.

[aantich]

Addressed all comments.

[jgm]

Tests are failing - can you fix?

[jgm]

Hi, just wanted to see if you're planning to finish polishing this up. I think the CI test failure is something trivial; this is close to being mergeable.