Add mdbook setup for documentation

• Serve an mdbook setup on https://alpm/archlinux.page
• Move all rustdoc to its own namespace
• Move specification info from top-level README to mdbook setup for nicer link setup

Fixes #76 (closed)

alpm-buildinfo/README.md

@@ -6,7 +6,7 @@ A library and commandline toolkit for the specification, writing and parsing of
 
 ## Documentation
 
-- <https://alpm.archlinux.page/alpm_buildinfo/> for development version of the crate
+- <https://alpm.archlinux.page/rustdoc/alpm_buildinfo/> for development version of the crate
 - <https://docs.rs/alpm-buildinfo/latest/alpm_buildinfo/> for released versions of the crate
 
 ## Examples