feat: relative and absolute links

[CatalinPlesu]

(cherry picked from commit 0c6ef0d87c7889769a2bf43b29607ef91f0ff5e3)

Previously all links were absolute (in my experience at least) Were added this cases: relative link, like (file.md), (./file.md) and (../file.md) but you can't get out of the wiki directory. And absolute path like this (/file.md) for the root of this wiki. probably isn't the markdown way to do it

[serenevoid]

We might need to add Windows support too. I'll look into this over the weekend

[CatalinPlesu]

My guess was that it should work. I used same joinpath function as before. And markdown has links like in the web with slash / not backslash \