Check for .md file existence on link click.

[CDOApps]

Closes #1085

[FranklinYu]

I like the idea, but in this case we can be more aggressive. For bare path without file extension like [this][file-name], I think we can simply create file-name.md. This is not necessarily .md; if I recall correctly user can specify a preferred extension.

[CDOApps]

I like the idea, but in this case we can be more aggressive. For bare path without file extension like [this][file-name], I think we can simply create file-name.md.

Tell me if I'm wrong, isn't what MacDown's doing if the file doesn't exist?

This is not necessarily .md; if I recall correctly user can specify a preferred extension.

I didn't see where to define a preferred extension but it sounds better than using hard coded .md for extension. Actually, I based my solution on the prepareSavePanel: which fills the path with .md if the file name is not using this for extension.

[FranklinYu]

@CDOApps Oh then maybe MacDown is already doing that. In that case we can merge this as-is. Let me check this week when I get back to my Mac… Currently using Windows.

[uranusjr]

Maybe we can check for more stuffs (e.g. check for UTI instead of extension, but this good enough as-is.