Improve axes and tick behaviour, add surrounding axes.

Ticks are calculated more robustly.

Axes now surround the plot, rather than being only at the bottom and left, and ticks are positioned inside the plot. For example, the old behaviour:

![Old axes and ticks](https://cloud.githubusercontent.com/assets/540853/3130009/a511d610-e7ef-11e3-86dc-271049e14f3a.png)

New behaviour:

![New axes and ticks](https://cloud.githubusercontent.com/assets/540853/3130010/a789fb3e-e7ef-11e3-937e-70332296599e.png)

This brings the default look more inline with the ROOT style, as per #3.