Replace data URIs with font arrows.

data-uris violate the CSP style-src: 'self'.
Merge pull request #158 from graingert/patch-1

Replace data URIs with font arrows.
added missing parenthesis
Merge pull request #164 from benfoxall/patch-1

Readme tweak - missing ")"
Revert "Replace data URIs with font arrows."

This reverts commit 40956076ad6b99b2fd43b87ec005711a1325b602.