Replaces in fills in a svg file with hatching
according to lightness.

Eggbots hatching plugin needs to be installed,
preferably in ~/.config/inkscape/extensions

http://wiki.evilmadscientist.com/The_Eggbot_Extensions


KNOWN ISSUES:

- transform for complete layers will not be copied
- needs fill
- define end of header unclear </metadata> or </defs>
  </defs> does not exist when defs are empty