Pdpinch/documentation updates

All the docs, including installation and course author documentation, are in the ReadMe now. 
I thought you might mention that. ;) Off the top of your head, is there any reason that baking a Set of referenced xblocks on course import (and updated/maintained if/when edits are made with studio), maybe during the validation phase, and storing it as course metadata, would be impractical? The only issue I can see is that studio would have no way of knowing if the course is still dependent on an xblock after deleting a module without querying all of the course content, but it seems that can be solved with simple reference counting... probably way more hairy to implement than it sounds though.