This fixes #7. Cleanup to come.

Now that I understand the solution, I'm going to roll it into a clean
loop, but I want to save the current explicit implementation for posterity.
Cleanup and mostly fixed #6

Rolled the previous implementation into a cleaner loop, and inserted a
2,4,6,8 level while I was at it. The tick labels still overlap at times,
but it's much better than it was. Fully solving #6 will take a bit more
work. I might be able to get away with simply always hiding the
sub-minor tick labels, though.
Hid subminor ticklabels, completely fixing #6

Only issue remaining is that there are too few ticks at the wider zoom
levels. I'll have to override tickValues to fix that.
Improved LogAxis tick labels
Fixed small bug and improved tick spacing.

This should be it for LogAxis.
Merge branch 'iss7' into develop