Update zstd to 1.3.0

[elijahandrews]

No description provided.

[Viq111]

lgtm

Benchmarks (same payload as #1):

Current branch:
local:~/datadog/zstd (1.x✔) ᐅ eval "$(gimme 1.8.3)"
go version go1.8.3 darwin/amd64
local:~/datadog/zstd (1.x✔) ᐅ go test -bench . -benchtime 10s
BenchmarkStreamCompression-4             100     130811864 ns/op      76.22 MB/s
BenchmarkStreamDecompression-4           500      32245337 ns/op     309.21 MB/s
BenchmarkCompression-4                   100     119040542 ns/op      83.76 MB/s
BenchmarkDecompression-4                1000      21742581 ns/op     458.57 MB/s
--- BENCH: BenchmarkDecompression-4
    zstd_test.go:156: Reduced from 9970564 to 3444121
    zstd_test.go:156: Reduced from 9970564 to 3444121
    zstd_test.go:156: Reduced from 9970564 to 3444121

local:~/datadog/zstd (1.x✔) ᐅ eval "$(gimme 1.9rc2)"
go version go1.9rc2 darwin/amd64
local:~/datadog/zstd (1.x✔) ᐅ go test -bench . -benchtime 10s
goos: darwin
goarch: amd64
BenchmarkStreamCompression-4             100     122424710 ns/op      81.44 MB/s
BenchmarkStreamDecompression-4           500      31619403 ns/op     315.33 MB/s
BenchmarkCompression-4                   100     118267762 ns/op      84.31 MB/s
BenchmarkDecompression-4                 500      22691712 ns/op     439.39 MB/s
--- BENCH: BenchmarkDecompression-4
    zstd_test.go:156: Reduced from 9970564 to 3444121
    zstd_test.go:156: Reduced from 9970564 to 3444121
    zstd_test.go:156: Reduced from 9970564 to 3444121


Your branch (zstd 1.3.0):
local:~/datadog/zstd (elijah/1.3.0✔) ᐅ eval "$(gimme 1.8.3)"
go version go1.8.3 darwin/amd64
local:~/datadog/zstd (elijah/1.3.0✔) ᐅ go test -bench . -benchtime 10s
BenchmarkStreamCompression-4             100     133005398 ns/op      74.96 MB/s
BenchmarkStreamDecompression-4           500      31422800 ns/op     317.30 MB/s
BenchmarkCompression-4                   100     126352613 ns/op      78.91 MB/s
BenchmarkDecompression-4                1000      20781138 ns/op     479.79 MB/s
--- BENCH: BenchmarkDecompression-4
    zstd_test.go:156: Reduced from 9970564 to 3429982
    zstd_test.go:156: Reduced from 9970564 to 3429982
    zstd_test.go:156: Reduced from 9970564 to 3429982

local:~/datadog/zstd (elijah/1.3.0✔) ᐅ eval "$(gimme 1.9rc2)"
go version go1.9rc2 darwin/amd64
local:~/datadog/zstd (elijah/1.3.0✔) ᐅ go test -bench . -benchtime 10s
goos: darwin
goarch: amd64
BenchmarkStreamCompression-4             100     143386144 ns/op      69.54 MB/s
BenchmarkStreamDecompression-4           500      31575229 ns/op     315.77 MB/s
BenchmarkCompression-4                   100     128747846 ns/op      77.44 MB/s
BenchmarkDecompression-4                1000      20747701 ns/op     480.56 MB/s
--- BENCH: BenchmarkDecompression-4
    zstd_test.go:156: Reduced from 9970564 to 3429982
    zstd_test.go:156: Reduced from 9970564 to 3429982
    zstd_test.go:156: Reduced from 9970564 to 3429982

So overall compression seems a tiny bit slower (~2-5%), decompression faster (~10%) and compression ratio (just tested on mr payload though) is roughtly the same (change: -0.4%)