Adding option for rounded top and vertical xlabels to morris.bar 

Added two small feature options with defaults to morris.bar: 

barShape: 'sharp'
verticalLabels: true

barShape defaults to the standard sharp rect top-of-bar shape, while 'soft' draws a smooth rounded path for the top-of-bar.

verticalLabels defaults to false, the standard horizontal implementation, but can be set to true for a 90degree rotation and 1/3 bounding box y-shift down.  This implementation isn't perfect but can allow for xlabels in densely populated graphs (see included example bar-soft-verticalxlabel.html).