marker types using rbush for masking
fix typos
always render overlay when @select_every_mousemove is set
initial working-ish selection. Problems remaining:

* screen/device issue for selection coords
* selection tool should add and draw its own overly
* selection tool should be plot independent
 merged from master
Merge branch 'feature/selection' of github.com:ContinuumIO/bokeh into feature/selection
style
Merge branch 'master' into feature/selection
rbush missing from test harness
changed ready for circle that will accept radius or size
combined fixes:
* size defaults to screen units always
* circle accepts size or radius
* use 'vx' for view coordinates, rename mapping functions as needed
fix error in v_sy_to_vy, update comments
make drag end mouse coord computation consistent with everywhere else
fix for case when xrange or yrange is null
box selection now set selection geometry and call hittest
fix bug in rect, need to stroke after rect call, not before
mask is really a list of indices, not a boolean mask
loop over mask to plot points, will add data masking later
simplify square marker, don't inherit from rect, simplify other square markers, no need to keep width and height
fix up legend code