Add support for browserify.

This includes a new optional canvas accessor for use with Node.js, and
removes the dependency on a specific canvas library for Node.js.

Fixes #70, fixes #72, and fixes #76.

.gitignore

@@ -1 +1,2 @@
 node_modules
+npm-debug.log

.npmignore

@@ -0,0 +1 @@
+build

README.md

@@ -155,3 +155,16 @@ the spiral for each word.  This should return a number in the range `[0, 1)`.
 
 If not specified, returns the current random number generator, which defaults
 to `Math.random`.
+
+<a name="canvas" href="#canvas">#</a> <b>canvas</b>([<i>canvas</i>])
+
+If specified, sets the **canvas** generator function, which is used internally
+to draw text.  If not specified, returns the current generator function, which
+defaults to:
+
+```js
+function() { return document.createElement("canvas"); }
+```
+
+When using Node.js, you will almost definitely override this default, e.g.
+using the [canvas module](https://www.npmjs.com/package/canvas).

bower.json

@@ -1,18 +1,14 @@
 {
   "name": "d3-cloud",
-  "version": "1.1.2",
-  "main": "d3.layout.cloud.js",
-  "scripts": [
-    "d3.layout.cloud.js"
-  ],
+  "version": "1.2.0",
+  "main": "build/d3.layout.cloud.js",
   "ignore": [
     ".DS_Store",
     ".git",
     ".gitignore",
     ".npmignore",
     "examples",
     "index.js",
-    "lib",
     "node_modules",
     "package.json"
   ]