Safari snaps fonts to whole pixel sizes

Unfortunately for `TightenText`, Safari rounds font sizes to whole pixels as soon as it crosses the half-pixel boundary. This leads to a significant jump in how wide the text is, and also potentially means the resulting text is smaller than the developer's desired `minFontSize` (if, say, they want it to be 0.97 ems, and that results in a font size of 15.49px, Safari will render 15px text).

Some options:

1. Add a disclaimer for Safari.
2. Detect pixel rounding, refuse to cross the half pixel boundary if using such a browser.
3. Scale the font some other way (e.g. `transform`) that would achieve the same visual effect as the `font-size` change?