Strip more international punctuation characters from header ids in `ghCompatibleHeaderId` mode

[tunetheweb]

GitHub currently strips the following extended punctuation characters when creating headers in markdown files, but Showdown does not.

• Inverted exclamation and question marks (¡ and ¿) - used in Spanish
• Various full width punctuation marks (e.g. ？, ：...etc) - used a lot in Japanese

Evidence in this gist: https://gist.github.com/tunetheweb/ecbfed99663425a668748770568bdafb#some-header-with--chars

Seems an easy enough fix to add these so will submit a PR.

[tivie]

Hey.

Do you mean GitHub strips these characters from ids?

[tunetheweb]

Correct. If you look at that gist example (markdown gists automatically creates ids) you see it:

[tivie]

Thank you. Will be merging the PR.