Benchmark current performance against the competition

[hurrymaplelad]

Prompted by #48. Curious how performance stacks up today? Try npm run benchmark. Here's what I see:

teacup x 19,922 ops/sec ±1.44% (93 runs sampled)  
jade x 30,992 ops/sec ±0.65% (91 runs sampled)
underscore x 158,144 ops/sec ±0.86% (92 runs sampled)
underscore (no with) x 903,490 ops/sec ±0.66% (93 runs sampled)
dot x 460,082 ops/sec ±0.55% (92 runs sampled)

Jade is 1.5x faster. Underscore, used optimally, is 45x faster. Dot is 23x faster, and no longer the fastest on the block.

CoffeeCup saw a 10x speedup with a complex source transformation, suggesting we could get within 5x of underscore.

Based on these rough numbers, our pages would have to be ~1000x more complicated than the test page before we see template rendering on the order of 50ms.