Added support for SVGZ (i.e. GZIPed SVG).

This is based on work by josefpavlik (https://github.com/josefpavlik/svg-android/commit/fc0522b2e1). However I made an improvement by decorating the InputStream with a BufferedInputStream when mark/reset are not supported.

Signed-off-by: Matthias Stevens <matthias.stevens@gmail.com>