LPS-47908 markdown converter util

Hey Brian,

This pull is the code necessary to process markdown that will be used by knowledge base portlet. We need to merge this in because it's necessary for the deploy of the developer site on Friday.

@migue helped me to create this as an OSGI module although we may just use the jar in the knowledge base portlet to deploy it on developer site by friday.

We needed to include LiferayParser in org.pegdown as part of this commiet https://github.com/sergiogonzalez/liferay-portal/commit/f5aef2171df364629517ca9dd75fca4ec5a485fe because it's a limitation of the pegdown third party library. Otherwise it won't work throwing an exception.

cc/ @jorgeferrer @jhinkey