Hide wiki markup as part of markdown-toggle-markup-hiding

[jayemar]

When markup hiding is enabled, the markup for markdown-style links is hidden, but the markup for wiki links is not. This code change fontifies the different sections of wiki links so that they are properly supported by markdown-toggle-markup-hiding.

Related Issues

The changes address issues #557, #782, and #847.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the CONTRIBUTING.md document.
• I have updated the documentation in the README.md file if necessary.
• I have added an entry to CHANGES.md.
• I have added tests to cover my changes.
• All new and existing tests passed (using make test).

[syohex]

• Please fix all byte-compile warnings
• Please add unit tests

[jayemar]

I fixed the byte compiler warnings and updated the wiki link tests to check that the face properties are properly being set to support markup hiding. I think I've done everything that's called out in CONTRIBUTING.md, but if not let me know.

Wiki links seemed to be handled very different front inline and reference links. I couldn't find a reason for the two different approaches, and it make some of the implementation more difficult than it needed to be, so some of my changes have the effect of treating wiki links much more like reference and inline links. If I misunderstood this and there's a reason for the two different approaches please let me know. (That's only if markdown-enable-wiki-links is t; otherwise they'll still ignored.)