This commit alters the way in which the Powerpoint writer treats
inline code and code blocks.
- Inline code is now formatted at the same size as the surrounding
text.
- Code blocks are now given a margin and font size according to their
level.
- Furthermore this commit allows changing the font with which code is
formatted via the `monofont` option.
Tested in
- PowerPoint 365 for Windows - 1808 (Build 10730.20344 Click-to-Run)
- PowerPoint 365 for Mac - 16.26 (19060901)
