* use a global sharded pool of proto.Buffer caches in protoCodec
* fix goimports
* make global buffer pool index counter atomic
* hack to remove alloc in encode_len_struct
* remove extra slice alloc in proto codec marshal
* replce magic number for proto size field length with constant
* replace custom cache with sync.Pool
* remove 1 line functions in codec.go and add protoCodec microbenchmarks
* add concurrent usage test for protoCodec
* fix golint.gofmt,goimport checks
* fix issues in codec.go and codec_test.go
* use go parallel benchmark helpers
* replace proto.Codec with a guess of size needed
* update Fatalf -> Errorf in tests
* wrap proto.Buffer along with cached last size into larger struct for pool use
* make wrapped proto buffer only a literal
* fix style and imports
* move b.Run into inner function
* reverse micro benchmark op order to unmarshal-marshal and fix benchmark setup-in-test bug
* add test for large message
* remove use of defer in codec.marshal
* revert recent changes to codec bencmarks
* move sub-benchmarks into >= go-1.7 only file
* add commentfor marshaler and tweak benchmark subtests for easier usage
* move build tag for go1.7 on benchmarks to inside file
* move build tag to top of file
* comment Codec, embed proto.Buffer into cached struct and add an int32 cap
apolcyn