Link to blob instead of linking to wiki.
Wiki will show relative links related to the wiki gollum repository.
Update wiki tests.
Update markdown documentation, fix wiki spec.
 Merge branch 'links_within_same_repo' into 'master'

Relative links within one system

When using relative links in md in repository file it will only link within the repository.
When using relative links in md in wiki page, it will only link to wiki pages.