add SVG image Support

[naitoh]

add SVG image Support

Method ImageSVG() was added to embedd SVG images (see example n. 6, 39, 58), using REXML for XML parsing. Note that not all SVG images are supported.

• Filter attribute of the g tag are not supported. See: https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Filter_effects
• use tag are not supported. See: https://developer.mozilla.org/en-US/docs/Web/SVG/Element/use

List of confirmed SVG files.

• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/410.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/git.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/gnome2.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/google.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/heart.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/heliocentric.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/hg0.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/http.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/ibm.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/ietf.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/ielock.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/mozilla.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/paths-data-08-t.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/python.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/rails.svg
• [x] https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/ruby.svg

List of unsupported SVG files

• Filter attribute
  • https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/gaussian1.svg
• use tag
  • https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/svg.svg