Improving test environment with expect.js, karma and Sauce Labs

Using:
 - expect.js (instead of chai) as it is also compatible with
   old versions of IE
 - karma which is the new version of testacular
 - Sauce Labs to automatically test noder on several browsers
Loader plugins
Allowing the resolver and loader to be configured at run time.
Improving configuration of built-in modules.
Improving build time by avoiding rebuilds of the bootstrap package.
Allowing the error context configuration to be customized.
Making asyncRequire simpler to use (non backward compatible).

This commit changes the API of asyncRequire.

Old usage (no longer valid):

asyncRequire(["a","b"]).then(function() {
   var a = asyncRequire("a");
   var b = asyncRequire("b");
   // use a and b
});

New usage:

asyncRequire("a","b").then(function(a,b) {
   // use a and b
});
1.2.0-rc0