Merge pull request #4 from kbroman/master

Fix alignment for left position
add ignore file
use bower for d3-tip and dependencies
update examples to use d3 component
improve bar example
:fire: it down
we no longer need padding, cornerRadius and stemSize
show tip with evaluated text
append text to the tooltip
use transformation matrix based on user screen to determine bbox
handle circle elements
kill some examples we no longer need
basic positioning
basic top center rect positioning
add n, s, e, and w to the bbox system
use new coordinate system to position tip
flesh out top and bottom orients
rename orient, use direction instead
move directions to methods out of tip.show
greatly simplify bounding box calculations