use our internal apply helpers everywhere

Thanks @jdalton for the suggestion. Provides a small but significant speed boost in `.bind()`, `.partial()` and `.partialConstructor()`. We still get our asses kicked by SpiderMonkey for prebound functions, but it's still faster than before:

#### V8
```
  Native .bind() vs fast.bind()
    ✓  Function::bind() x 832,970 ops/sec ±1.44% (85 runs sampled)
    ✓  fast.bind() x 7,142,465 ops/sec ±0.91% (93 runs sampled)
    ✓  fast.bind() v0.0.2 x 6,376,371 ops/sec ±1.14% (88 runs sampled)
    ✓  underscore.bind() x 528,686 ops/sec ±1.57% (80 runs sampled)
    ✓  lodash.bind() x 349,213 ops/sec ±2.10% (80 runs sampled)

    Result: fast.js is 757.47% faster than Function::bind().

  Native .bind() vs fast.bind() with prebound functions
    ✓  Function::bind() x 4,596,421 ops/sec ±1.05% (93 runs sampled)
    ✓  fast.bind() x 19,187,335 ops/sec ±0.97% (87 runs sampled)
    ✓  fast.bind() v0.0.2 x 13,930,265 ops/sec ±0.94% (89 runs sampled)
    ✓  underscore.bind() x 4,562,916 ops/sec ±0.95% (86 runs sampled)
    ✓  lodash.bind() x 4,860,192 ops/sec ±1.17% (87 runs sampled)

    Result: fast.js is 317.44% faster than Function::bind().

  Native .bind() vs fast.partial()
    ✓  Function::bind() x 841,061 ops/sec ±1.83% (80 runs sampled)
    ✓  fast.partial() x 8,674,420 ops/sec ±1.54% (93 runs sampled)
    ✓  fast.partial() v0.0.2 x 7,056,606 ops/sec ±1.43% (87 runs sampled)
    ✓  fast.partial() v0.0.0 x 6,806,520 ops/sec ±1.31% (87 runs sampled)
    ✓  underscore.partial() x 1,629,855 ops/sec ±1.49% (90 runs sampled)
    ✓  lodash.partial() x 329,820 ops/sec ±2.75% (69 runs sampled)

    Result: fast.js is 931.37% faster than Function::bind().

  Native .bind() vs fast.partial() with prebound functions
    ✓  Function::bind() x 4,362,196 ops/sec ±1.54% (91 runs sampled)
    ✓  fast.partial() x 18,008,835 ops/sec ±1.37% (73 runs sampled)
    ✓  fast.partial() v0.0.2 x 13,511,525 ops/sec ±1.40% (82 runs sampled)
    ✓  fast.partial() v0.0.0 x 13,379,174 ops/sec ±1.53% (78 runs sampled)
    ✓  underscore.partial() x 6,610,677 ops/sec ±1.25% (91 runs sampled)
    ✓  lodash.partial() x 4,630,166 ops/sec ±1.36% (87 runs sampled)

    Result: fast.js is 312.84% faster than Function::bind().

```
#### SpiderMonkey
```
  Native .bind() vs fast.bind()
    ✓  Function::bind() x 1,052,708 ops/sec ±3.17% (52 runs sampled)
    ✓  fast.bind() x 1,998,159 ops/sec ±2.90% (58 runs sampled)
    ✓  fast.bind() v0.0.2 x 850,026 ops/sec ±2.40% (63 runs sampled)
    ✓  underscore.bind() x 491,642 ops/sec ±3.26% (56 runs sampled)
    ✓  lodash.bind() x 255,096 ops/sec ±2.15% (62 runs sampled)

    Result: fast.js is 89.81% faster than Function::bind().

  Native .bind() vs fast.bind() with prebound functions
    ✓  Function::bind() x 75,606,163 ops/sec ±0.51% (68 runs sampled)
    ✓  fast.bind() x 9,952,095 ops/sec ±0.55% (67 runs sampled)
    ✓  fast.bind() v0.0.2 x 4,535,786 ops/sec ±1.13% (66 runs sampled)
    ✓  underscore.bind() x 74,498,853 ops/sec ±0.59% (67 runs sampled)
    ✓  lodash.bind() x 1,680,624 ops/sec ±2.38% (64 runs sampled)

    Result: fast.js is 86.84% slower than Function::bind().

  Native .bind() vs fast.partial()
    ✓  Function::bind() x 1,105,650 ops/sec ±3.08% (52 runs sampled)
    ✓  fast.partial() x 2,245,123 ops/sec ±3.01% (60 runs sampled)
    ✓  fast.partial() v0.0.2 x 917,150 ops/sec ±2.15% (64 runs sampled)
    ✓  fast.partial() v0.0.0 x 916,274 ops/sec ±2.28% (62 runs sampled)
    ✓  underscore.partial() x 818,945 ops/sec ±1.93% (60 runs sampled)
    ✓  lodash.partial() x 263,751 ops/sec ±2.30% (62 runs sampled)

    Result: fast.js is 103.06% faster than Function::bind().

  Native .bind() vs fast.partial() with prebound functions
    ✓  Function::bind() x 78,707,103 ops/sec ±0.33% (69 runs sampled)
    ✓  fast.partial() x 9,642,861 ops/sec ±0.43% (66 runs sampled)
    ✓  fast.partial() v0.0.2 x 4,203,013 ops/sec ±1.27% (40 runs sampled)
    ✓  fast.partial() v0.0.0 x 4,162,810 ops/sec ±0.82% (67 runs sampled)
    ✓  underscore.partial() x 3,163,519 ops/sec ±0.46% (68 runs sampled)
    ✓  lodash.partial() x 1,593,738 ops/sec ±2.59% (61 runs sampled)

    Result: fast.js is 87.75% slower than Function::bind().

```

fixes #49 
competing against underscore and Lo-Dash was never the goal and I don't want to imply that fast.js is a competitor to those libraries, we'll never have `fast.template()` for instance. It's not fair to say that we're including Lo-Dash in the marketing, we include it in the benchmarks because someone kindly provided a pull request, and some people find the comparison interesting. 

> Were you aware of Lo-Dash & its approach before you started?

Of course! but I'm writing a load of standalone libraries and don't want Lo-Dash (or anything else) as a dependency. In fact so far I'm not even including fast.js in those libraries, I'm just incorporating the parts of it that I need where I need them. 

> if Lo-Dash takes away the perf angle from fast, & does so without micro-optimizations, what does fast have left to offer?

Well, if this happens, it will be interesting, right? Would you have considered doing this if fast.js or something else had not come along and stepped on your territory? If you do this, everyone benefits. 

However, I think you downplay the impact of "micro-optimisations" because your library has an overall broader scope than fast.js (consistency, features, performance vs solely performance), the original intent here is to go fast in node, whereas you must consider every browser and various differences between them. Our focus is much narrower and therefore I think you'll struggle to close the gap. Anyway, please go ahead, I'm sure we'll all learn a lot :smile: