Added protection attributes.
Added Public API and Versionning Policy to readme file.
Merge branch 'extra' into lib-protected

Conflicts:
	Michelf/Markdown.php
	Readme.md
Fixed readme to include information about beta 5.
Added protected visibility attribute to a few new functions coming from the extra branch.
Updates to readme file.
Merge branch 'lib-protected' into lib

Conflicts:
	Readme.md