Convert README to Markdown.

Conflicts:
	README.md
Add Travis CI build status badge to README.
Travis CI integration.
Test against 5.2.3, our minimum version.
Also test against 5.3, 5.4 and 5.5 to be forward looking
Travis doesn't have PHP 5.2.3.  Test against 5.3 / 5.4 / 5.5.
Follow-on for #2043.  Fix some tests that made bad assumptions about
the state of the world.  These were uncovered when we ran the tests on
Travis which runs the tests in a different order than what I (and
apparently others) use on their dev boxes.