Apply floor/ceiling to axis-extent before upper_/lower_buffer (#90)
Apply floor/ceiling to axis-extent before upper_/lower_buffer (#90)

* Avoid upside-down axes when using floor/ceiling by setting the un-overridden end to min/max of extent

* Apply floor/ceiling before upper_buffer/lower_buffer

* Simplify extent code

statgen/locuszoom,statgen/locuszoom,statgen/locuszoom