Improve tick-count setting API.

Now, ticks(count) sets the number of ticks and returns the
calling QuantitiveScale, instead of setting the number of ticks
and returning that many ticks.

API breaking change.

Close #1057.
Continuing to push change to (default = this.numTicks())

I'll harden the default documentation once I get to it, since it doesn't seem that typedoc will doc this part specifically.