md2pptx crashes with `sectionsExpand: yes` if section title contains emoji or ampersand

[MartinPacker]

Attempt to parse XML fails.

The section title gets created with sectionsExpand: no but sectionsExpand: yes causes md2pptx to fail.

Fix is to only allow certain characters to be used in the XML attribute for section name. Currrently coded fix allows:

• Alphanumerics
• Spaces

[MartinPacker]

Added

• Minus sign (or dash)
• Conversion of <br/> to space
• & with a following space

[MartinPacker]

Added

• +
• /

[MartinPacker]

Added

• * - through ∗ (otherwise it gets confused with bold or italic emphasis.

[MartinPacker]

Fixed and shipped in v3.3.2.