Added lineHeight to the font-spec object.

Line height is a core font property - it can be specified as part of the
unified 'font' definition - and we therefore need to give users access
to it when they're manually defining the font.

API.md

@@ -298,6 +298,7 @@ with this format:
 ```js
 {
     size: 11,
+    lineHeight: 13,
     style: "italic",
     weight: "bold",
     family: "sans-serif",
@@ -306,6 +307,9 @@ with this format:
 }
 ```
 
+The size and lineHeight must be expressed in pixels; CSS units such as 'em'
+or 'smaller' are not allowed.
+
 The options "min"/"max" are the precise minimum/maximum value on the
 scale. If you don't specify either of them, a value will automatically
 be chosen based on the minimum/maximum data values. Note that Flot

jquery.flot.js

@@ -286,7 +286,7 @@ Licensed under the MIT license.
 		// If the font is a font-spec object, generate a CSS font definition
 
 		if (typeof font === "object") {
-			textStyle = font.style + " " + font.variant + " " + font.weight + " " + font.size + "px " + font.family;
+			textStyle = font.style + " " + font.variant + " " + font.weight + " " + font.size + "px/" + font.lineHeight + "px " + font.family;
 		} else {
 			textStyle = font;
 		}
@@ -453,7 +453,7 @@ Licensed under the MIT license.
                     show: null, // null = auto-detect, true = always, false = never
                     position: "bottom", // or "top"
                     mode: null, // null or "time"
-                    font: null, // null (derived from CSS in placeholder) or object like { size: 11, style: "italic", weight: "bold", family: "sans-serif", variant: "small-caps" }
+                    font: null, // null (derived from CSS in placeholder) or object like { size: 11, lineHeight: 13, style: "italic", weight: "bold", family: "sans-serif", variant: "small-caps" }
                     color: null, // base color, labels, ticks
                     tickColor: null, // possibly different color of ticks, e.g. "rgba(0,0,0,0.15)"
                     transform: null, // null or f: number -> number to transform axis
@@ -672,6 +672,8 @@ Licensed under the MIT license.
                     family: placeholder.css("font-family")
                 };
 
+            fontDefaults.lineHeight = fontDefaults.size * 1.15;
+
             axisCount = options.xaxes.length || 1;
             for (i = 0; i < axisCount; ++i) {