Merge branch 'bc/asciidoctor'

Add machinery to alternatively use AsciiDoctor to format our
documentation.

* bc/asciidoctor:
Documentation: remove Asciidoctor linkgit macro
Documentation: refactor common operations into variables
Documentation: implement linkgit macro for Asciidoctor
Documentation: move some AsciiDoc parameters into variables

diff --cc Documentation/Makefile
Simple merge