Added HtmlGraphics.registerFontMetrics for overriding font line height.
Added HtmlGraphics.registerFontMetrics for overriding font line height.

Font measurement in HTML5 is a giant hack, and it's not super surprising that
browsers return wildly different values for the height of a line of text. This
allows a game to override the measured values and just use a value that is
consistent and will actually result in sanely rendered text across browsers.

playn/playn,tinkerstudent/playn,ruslansennov/playn2,longtaoge/playn,ruslansennov/playn2,playn/playn,thecocce/playn-1,tinkerstudent/playn,rachelharvey/playn,playn/playn,rachelharvey/playn,thecocce/playn-1,longtaoge/playn