Merge pull request #1 from tmjbradley/master

Remove deprecated cudaThreadSynchronize()
Update exercise.cu
Add first stab at introduction for README for the quad tree exercise.
Merge pull request #2 from tmjbradley/master

Added more_points exercise
Move the definition of bbox to util.h
Encapsulate point->tag transformation into point_to_tag function.
Narrate up to the first reduction
Narrate up to the sort
Add the parallel part of the "Linearizing the Points" section
Some small edits