Choose arrow shaft-width via inspector.
Cleanup warnings.

o import is a reserved word.
o IDEA thinks that catch blocks should bind the exception.
Draw arrows as filled outline instead of line with end marker.

The SVG end marker design is quite poor. In particular, markers don't inherit
any styling from the lines to which they are applied.
Therefore, we calculate the shape of the arrowheads in code and render a
single outline instead of a line plus marker.