Performance optimizations for dynamic function execution.

[benjchristensen]

• memoize dynamic function constructions so executions are statically typed after a single dynamic lookup instead of dynamic on every execution

#104

[benjchristensen]

Test case:

    public void runCompositionTest(Integer[] values) {
        System.out.println("runCompositionTest");

        final AtomicInteger onNextSum = new AtomicInteger(0);
        final long start = System.nanoTime();

        MathFunction m = new MathFunction();
        // 50 levels of composition (same function so that's not the cost)
        Observable.from(values)
                .map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m)
                .map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m)
                .map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m)
                .map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m)
                .map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m).map(m)
                .subscribe(new TestObserver(onNextSum, start));
    }

Before this commit:

Sum: 710082754 Time: 437.936ms

After this commit:

Sum: 710082754 Time: 60.605ms