Relying on window.devicePixelRatio causing issues when browser is zoomed

[cfx1]

Tested on Firefox 38 and Chrome 42.0.2311.152 with Tinycon 0.6.3

If the page utilizing Tinycon is zoomed in (eg. Ctrl +), Tinycon's use of window.devicePixelRatio will cause the text to be drawn off-center depending on the level of zoom. Apparently using window.devicePixelRatio is not reliable because it is directly affected by the zoom level of the browser, which can change from user to user.

Firefox discussion: https://bugzilla.mozilla.org/show_bug.cgi?id=809788
Stackoverflow discussion: http://stackoverflow.com/questions/16541676/what-are-best-practices-for-detecting-pixel-ratio-density