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
Merge pull request #143 from mojavelinux/revise-readme

Revise readme