layouts: move page title outside #page-content
update docs submodule

Add styles for new docs page.
move API-independent files in this repo

Pull the latest changes from the submodule (removal of independent pages)
and add the removed pages here, along with a new index page.
adjust docs link in default layout
add overflow-handling to code boxes
better title for docs index page
correct link in index file to docs
add ability of sub-links in navigation and add such for API docs
style fix: only elements directly under #page-content are indented
once more update the docs
avoid unnecessary header duplication for blog
decrease blog header levels
add sitemap file