Improved selection of log-scale ticks

The algorithm for selecting log-scale ticks (on powers of ten) has been improved. In particular, it will now always draw as many ticks as possible (e.g., it will not draw a single tick if it was possible to fit two ticks); if subsampling ticks, it will prefer putting ticks on integer multiples of the subsampling stride (e.g., it prefers putting ticks at 10⁰, 10³, 10⁶ rather than 10¹, 10⁴, 10⁷) if this results in the same number of ticks at the end; and it is now more robust against floating-point calculation errors.