Merge: nitiwiki: introduce wikilinks

Nitiwiki now understand the wikilink format using double brackets.

Examples:
`[[foo]]`: link to the page named `foo`
`[[foo/bar]]`: link to the page named `bar` in `foo`
`[[/foo/bar]]`: link to the page located exactly here

It's also possible to add a custom name:
`[[foo|My cute custom name <3]]`: link to the page named `foo`

And to use anchors:
`[[foo#bar]]`: link to the page named `foo`

nitiwiki will display warnings if a link seems broken.

Pull-Request: #1317
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>