licensing and acknowledgement

fixes #34
Update README.md
Merge branch 'master' of git://github.com/cebe/markdown into cebe-master

Conflicts:
	GithubMarkdown.php
	Markdown.php
	Parser.php
	bin/markdown
	tests/BaseMarkdownTest.php
	tests/GithubMarkdownTest.php
	tests/MarkdownTest.php
	tests/profile.php