Fix broken links in the documentation

[Sahil1479]

There are links in the documentation (docs/) that are supposed to point/redirect to some other .md files, but currently, clicking those links gives the error 404.

Reason: Incorrect paths.

Example:
https://github.com/pgeu/pgeu-system/blob/master/docs/confreg/index.md

On this page, none of the links is accessible.

Also added support to have them viewable both in the help system and standalone on GitHub, as suggested in #64.

[Sahil1479]

@mhagander Could you please review this PR?

[Sahil1479]

Is there anything that I need to change?

[mhagander]

At least some links are still broken when viewed on gitub AFAICT. For example, going to the "Configuring a conference page", the very first link is a 404. So it probably needs another go-through of links to clean them up. Same thing in the payments documentation, has at least one broken link that needs to be fixed.

I'd really like it if we can get rid of the .md suffixes in the URls when rendered on the website, mainly because it just looks ugly :) Surely we can find some way to do that? If we want it compat with github, we probably need to put the md into the link in the file, but then remove it again when rendering in-site. This is not the end of the world if we can't figure it out, but it would be good to spent at least abit of time to see if we can do that.

And finally, in the regexp in urls, it should explicitly allow "nothing or .md", I think. And the current regexp is just plain wrong - it also allows .mx. Since a dot matches any character, not just the dot, and there's also no length limit.