Support solidColor element from SVG 2 #44
Description
Add solidColor element.
Implement parsing from XML and writing to XML.
Add test.
This element was introduced in SVG spec version 2. While this library aims to support SVG 1 for now, this element might be useful.
https://www.w3.org/TR/2013/WD-SVG2-20130409/pservers.html#SolidColors
Potential use case is to be able to change colors in SVG dynamically.