Sein Tao

add python3 support all strings are automatically treated as bytes under python2 and unicode under python3 all test passed under Python 2.7.10 and Python 3.5.1

The axis is not aligned if plot is with `coord_fixed()` or `theme(aspect.ratio = 1)`. example: ```r library(ggplot2) library(aplot) df = data.frame(x=rnorm(100), y=rnorm(100)) p.scatter = ggplot(df, aes(x=x, y=y)) + geom_point() p.xmargin...