Support media directly in markdown syntax

[rhukster]

Currently media functionality provides powerful image manipulation. http://learn.getgrav.org/content/media. However it requires twig tags, and twig processing to be enabled for a page. Ideally we would extend parsedown to translate local image references into media calls. This way it would be more readable, and editable in markdown editors, yet still providing the power of our media processing.

![Alt text](image1jpg?forceResize=200,200 "Optional title")

[rhukster]

Ok this support has been added. No more process: twig: true required on the page. All the media stuff is supported for example:

![Muertos Cat](muertos.jpg?cropResize=300,300 "Muertos OctoCat ")

![Iron Cat](ironcat.jpg?lightbox=900,900&cropResize=300,300&grayscale "Iron OctoCat ")

Even lightbox HTMl can be generated from this tag - pretty cool!