adds more HTML5 characters

adds:
 data https://developer.mozilla.org/en-US/docs/Web/HTML/Element/data
 menuitem https://developer.mozilla.org/en-US/docs/Web/HTML/Element/menuitem
 main https://developer.mozilla.org/en-US/docs/Web/HTML/Element/main
 math https://developer.mozilla.org/en-US/docs/Web/MathML/Element/math
 svg https://developer.mozilla.org/en-US/docs/Web/SVG/Element/svg
Merge pull request #1 from luxe/patch-1

adds more HTML5 characters