resolves #350 set Asciidoctor doc attributes

- set doc attributes: docfile, docdir, docname, etc
- implicitly sets base_dir (handled by Asciidoctor) for resolving paths
fix conflict between Asciidoctor and RSpec over Extensions constant
extend RSpec::Matchers to access expect()
Merge pull request #351 from mojavelinux/asciidoctor-base-dir

resolves #350 set Asciidoctor doc attributes