Major: Codegen changes for oj 2

[iccir]

This issue tracks codegen changes from oj 1 -> oj 2. These changes should be benign, but are significant enough that I wanted to wait for a major version bump.

[iccir]

In oj 1.x, @implementation Foo generates the following code:

var Foo = $oj_oj._registerClass({ $oj_c_Foo:1 }, null, function($oj_s, $oj_m) {
    function Foo() { this.constructor = Foo;this.$oj_id = ++$oj_oj._id; }
    $oj_m.$oj_f_isFoo = function() { return true; }

    return Foo;
});

The var Foo = $oj_oj._registerClass(… is an artifact from the oj 0.x days and results in false positives in ESLint (unused variables). The line should just be:

$oj_oj._registerClass({ $oj_c_Foo:1 }, null, function($oj_s, $oj_m) {

As Ingwie points out in #81, this variable is actually undefined due to _registerClass not returning anything.

[iccir]

oj 2.x now uses up to one temporary return variable per method invocation. This simplifies logic in the compiler and may allow certain optimizations by JS engines (reusing a variable can cause two different types to be assigned to it, which may deoptimize).

[iccir]

Closing for 2.0 release