Improve markdown parsing

* dont try to build links for anchors like `#title-anchor`
* dont build relative url for project with empty repo

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Change newlines in requirements doc.
Simplify the supported/unsupported sections of the requirements guide.
Merge branch 'improve-markdwon-render' into 'master'

Improve markdwon parsing

Fix 500 error when try to use relative links in project issues if repository is empty