Minimal example for drawing an isolated axis

This is the basic example of how to draw an axis alone -- without the whole
graph. It serves to simplify the following examples. ... The function
`pathaxis` from the `graph.axis` module takes a path and returns a canvas which
contains the drawn axis.

In contrast to the typical usecase of graphs containing data, we here have to
provide the range explicitly (using the `min` and `max` arguments). For real
graphs the range of an axis, of course, is adjusted automatically, although you
can still set minimal and/or maximal values to force a certain axis range.