Linking to documentation pages should be easier

[reitzig]

Say I have a file My Guide.md that I include in a custom category. I have to name it thus to that I get My Guide in the menu of the resulting doc.
(Side note: Instead of using the file name, use the first headline as page title?)

Now, linking to this guide should be as easy as writing

[this guide](My Guide)

or maybe

[this guide](My Guide.md).

Instead, we currently have to do

[this guide](my-guide.html)

This requires us to know exactly how slugs work (and possibly how folders are organized, if paths are more complicated). It's also not robust against changes in slugging.