Support newer svg elements

[macintoshhelper]

react-sketchapp and react-native-svg have more svg elements now:

{ ClipPath, Image, Pattern, TextPath, TSpan }

Should I go ahead and open a PR @chengyin ?

[chengyin]

@macintoshhelper Please feel free to send in a PR.

[macintoshhelper]

Thanks! Opened a PR, and added some docs to the README.md 🙂