remove .bind()... sadly, for efficiency's sake

ref #87, purely for the performance gain demonstrated by the benchmarks.

```
LevelUP           put(int, string) x 10 x 920 ops/sec ±0.63% (41 runs sampled)
LevelUP (release) put(int, string) x 10 x 916 ops/sec ±0.75% (32 runs sampled)

LevelUP           put(int, string) x 1000 x 186 ops/sec ±2.68% (70 runs sampled)
LevelUP (release) put(int, string) x 1000 x 115 ops/sec ±2.00% (80 runs sampled)

LevelUP           put(int, string) x 100,000 x 1.38 ops/sec ±22.51% (12 runs sampled)
LevelUP (release) put(int, string) x 100,000 x 0.94 ops/sec ±2.59% (9 runs sampled)

LevelUP           get(int):string x 10 x 927 ops/sec ±0.65% (21 runs sampled)
LevelUP (release) get(int):string x 10 x 911 ops/sec ±3.00% (18 runs sampled)

LevelUP           get(int):string x 1000 x 169 ops/sec ±2.58% (76 runs sampled)
LevelUP (release) get(int):string x 1000 x 160 ops/sec ±2.28% (75 runs sampled)

LevelUP           batch(int, string) x 1000 x 400 ops/sec ±2.41% (85 runs sampled)
LevelUP (release) batch(int, string) x 1000 x 397 ops/sec ±2.54% (85 runs sampled)

LevelUP           batch(int, string) x 100,000 x 2.21 ops/sec ±78.31% (8 runs sampled)
LevelUP (release) batch(int, string) x 100,000 x 3.42 ops/sec ±2.29% (8 runs sampled)
```