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 
@jdalton I'll confess that I didn't really have a game plan in mind when I pushed ~200 lines of code to a repo with a catchy name some time last week :). But I've been thinking about that, here are my goals with fast:

1. Make writing very fast JavaScript easier.

2. Serve as a reference implementation for people who're interested in very high performance JS patterns. This can be better achieved by fully describing each of the tradeoffs and shortcuts each fn uses in the comments. 

3. Shame browser vendors into improving their native implementations.


So let's say you decide to take all these functions and bundle them into Lo-Dash - *great* - that accomplishes 1. 

If browsers improve their builtins so that they consistently beat fast.js then *great* - everyone benefits.

I want to live in a world where `.forEach()` is just as fast as a for loop.