Ship CJS modules instead of browserified build

It turns out that if you try to browserify a file requiring react-tools,
it doesn't work. This is because browserify just visits the require
statements in the file and looks for files in that path.
./ReactCompositeComponent doesn't exist and that's the point that fails.
So the fix is to actually ship each of our CJS modules as individual
files like browserify expects. This should have no negative side effects
- we still only export React (though the rest of our modules are now
actually accessible, which might make it easier to do more with the
module).

The other change here is to move source-map to dependencies since it's
required in the transform code.

Test Plan:

```
$ npm pack .
$ cd /tmp
$ npm install path/to/react-tools-0.3.1.tgz
$ echo "require('react-tools')" > test.js
$ browserify test.js
```

Author: zpao

main.js

@@ -1,6 +1,6 @@
 'use strict';
 
-var React = require('./build/react');
+var React = require('./build/modules/React');
 var visitors = require('./vendor/fbtransform/visitors').transformVisitors;
 var transform = require('./vendor/fbtransform/lib/transform').transform;
 

package.json

@@ -16,7 +16,7 @@
     "README.md",
     "main.js",
     "bin/jsx",
-    "build/react.js",
+    "build/modules/",
     "vendor/fbtransform/",
     "vendor/woodchipper.js"
   ],
@@ -35,7 +35,8 @@
     "base62": "~0.1.1",
     "commoner": "~0.6.8",
     "esprima": "git://github.com/facebook/esprima#fb-harmony",
-    "recast": "~0.3.3"
+    "recast": "~0.3.3",
+    "source-map": "~0.1.22"
   },
   "devDependencies": {
     "browserify": "~2.14.2",
@@ -47,7 +48,6 @@
     "optimist": "~0.4.0",
     "phantomjs": ">= 1.9.0",
     "semver": ">= 1.1.4",
-    "source-map": "~0.1.22",
     "uglify-js": "~2.3.6",
     "grunt-contrib-clean": "~0.4.1",
     "grunt-compare-size": "~0.4.0",