add character encoding

[RossPaterson]

The W3C validator reports:

Warning: No Character encoding declared at document level

This could be fixed by prepending

<?xml version="1.0" encoding="UTF-8"?>

to the SVG output.

[fitnr]

Is there an example where the lack of an explicit character encoding is causing an issue?

[RossPaterson]

Not that I know of, but some people like to check files with the W3C Markup Validation Service, and it flags this as a warning, not an error like #11.