Xing share support

[AndrewLeedham]

Added support for Xing, the German social media platform.

I added the glyph to the SVG font then generated the TTF, WOFF and EOT files based on that. Not sure if this is the process you have been using. Let me know if not.

Tried to get the share_counter working for Xing, but they don't support CORS, so would most likely need some sort of iFrame hacking to get it working. Left it out for now.

I transpiled the CSS with lessc and minified the JS with uglify.js. Not sure what settings you use for lessc, just used -x.

Updated the docs to show basic Xing examples.

Closes: #53