assert: Make `assert` module an `assert.ok` function

Code can be written:

    var assert = require('assert');
    assert(true);

instead of:

    var assert = require('assert');
    assert.ok(true);

lib/assert.js

@@ -30,7 +30,7 @@ var pSlice = Array.prototype.slice;
 // AssertionError's when particular conditions are not met. The
 // assert module must conform to the following interface.
 
-var assert = exports;
+var assert = module.exports = ok;
 
 // 2. The AssertionError is defined in assert.
 // new assert.AssertionError({ message: message,
@@ -120,9 +120,10 @@ assert.fail = fail;
 // message_opt);. To test strictly for the value true, use
 // assert.strictEqual(true, guard, message_opt);.
 
-assert.ok = function ok(value, message) {
+function ok(value, message) {
   if (!!!value) fail(value, true, message, '==', assert.ok);
 };
+assert.ok = ok;
 
 // 5. The equality assertion tests shallow, coercive equality with
 // ==.