encoding/decoding performance

[cometkim]

Moved from #112

pbkit currently has very bad performance at encoding/decoding messages (~20 times worse than protobufjs)

pbkit encode      x  41,223 ops/sec ±0.35% (93 runs sampled)
protobufjs encode x 843,774 ops/sec ±0.51% (93 runs sampled)

pbkit decode      x  36,165 ops/sec ±0.94% (91 runs sampled)
protobufjs decode x 281,256 ops/sec ±0.40% (93 runs sampled)

It seems obvious that the Long constructor (dark-blue part in below screenshot), which does a lot of unnecessary work, is the bottleneck most of the time.

(left: pbkit, right: protobufjs)

(Bottom up chart)

You can check detail from this cpu profile snapshots:

pbkit-benchmarks-cpuprofiles.zip