New Markdown processor

[Nigel Charman]

I've created PR#272 to replace the Pegdown Markdown processor with Flexmark. This should be fully working as per the current Concordion spec. 

If you have Markdown specifications, I'd be keen for any feedback on how this update works for you.

If you are willing to try it out, you can use Jitpack to get the dependency, For example if using Gradle, add:

maven { url "https://jitpack.io" }

to your repositories, and update your Concordion dependency to use:

com.github.concordion:concordion:flexmark-SNAPSHOT

thanks

Nigel