change file extension of README to adoc
revise AsciiDoc syntax in README

- set java as default source language
- don't set language on Java source blocks
- only show build status image on GitHub
- use atx-style for document title
- rename *-url attributes to *-uri
- use implicit table headers
- make use of monospace formatting in table columns
- remove trailing whitespace from lines
fixes issue #142 by registering AsciidoctorJ modules so Java classes can be accessed better from Ruby.
Merge pull request #143 from mojavelinux/revise-readme

Revise readme
Merge branch 'master' of https://github.com/asciidoctor/asciidoctorj
resolves issue #118 by adding information about how to integrate AsciidoctorJ into JBoss Wildfly. Pull request could not be merged because of major changes written in issue #143
resolves issue #141 by renaming dom package to ast.