Update zstd to 1.1.3 for 1.x branch

[Viq111]

Straightforward C files update is available at this commit: 45f7613

Unfortunately that triggers some warnings on ZBUFF deprecation:

cgo-gcc-prolog:39:25: warning: 'ZBUFF_createDCtx' is deprecated: use ZSTD_createDStream [-Wdeprecated-declarations]
./zbuff.h:120:56: note: 'ZBUFF_createDCtx' has been explicitly marked deprecated here
cgo-gcc-prolog:60:6: warning: 'ZBUFF_decompressContinue' is deprecated: use ZSTD_decompressStream [-Wdeprecated-declarations]
./zbuff.h:126:54: note: 'ZBUFF_decompressContinue' has been explicitly marked deprecated here
cgo-gcc-prolog:77:6: warning: 'ZBUFF_decompressInit' is deprecated: use ZSTD_initDStream [-Wdeprecated-declarations]
./zbuff.h:123:59: note: 'ZBUFF_decompressInit' has been explicitly marked deprecated here
cgo-gcc-prolog:96:6: warning: 'ZBUFF_decompressInitDictionary' is deprecated: use ZSTD_initDStream_usingDict [-Wdeprecated-declarations]
./zbuff.h:124:59: note: 'ZBUFF_decompressInitDictionary' has been explicitly marked deprecated here
cgo-gcc-prolog:113:6: warning: 'ZBUFF_freeDCtx' is deprecated: use ZSTD_freeDStream [-Wdeprecated-declarations]
./zbuff.h:121:56: note: 'ZBUFF_freeDCtx' has been explicitly marked deprecated here
cgo-gcc-prolog:129:6: warning: 'ZBUFF_recommendedDInSize' is deprecated: use ZSTD_DStreamInSize [-Wdeprecated-declarations]
./zbuff.h:166:52: note: 'ZBUFF_recommendedDInSize' has been explicitly marked deprecated here
cgo-gcc-prolog:145:6: warning: 'ZBUFF_recommendedDOutSize' is deprecated: use ZSTD_DStreamOutSize [-Wdeprecated-declarations]
./zbuff.h:167:52: note: 'ZBUFF_recommendedDOutSize' has been explicitly marked deprecated here

I updated the bindings to the new interface here: 8ec87b6

Unfortunately (😞), this makes us use go pointers inside a C struct (ZSTD_inBuffer & ZSTD_outBuffer) so this needs compilation with GODEBUG=cgocheck=0
We will have to do memory management ourselves if we want to update to the new bindings.

panic: runtime error: cgo argument has Go pointer to Go pointer

However if you want to give it a go and need zstd 1.1.3, 45f7613 should be pretty stable (no bindings changes, it just add deprecation warnings)

Benchmarks (with mr):

ᐅ go version
go version go1.8 darwin/amd64

ᐅ git checkout 1.x
~/datadog/zstd (1.x) ᐅ go test -run no_test -bench .
BenchmarkStreamCompression-4     	    1000	 119786193 ns/op	  83.24 MB/s
BenchmarkStreamDecompression-4   	    3000	  34123937 ns/op	 292.19 MB/s
BenchmarkCompression-4           	    1000	 121966846 ns/op	  81.75 MB/s
BenchmarkDecompression-4         	    3000	  25224592 ns/op	 395.27 MB/s
	zstd_test.go:156: Reduced from 9970564 to 3444121

ᐅ git checkout 45f7613
~/datadog/zstd (45f7613) ᐅ go test -run no_test -bench .
BenchmarkStreamCompression-4     	    1000	 118444230 ns/op	  84.18 MB/s
BenchmarkStreamDecompression-4   	    3000	  36405709 ns/op	 273.87 MB/s
BenchmarkCompression-4           	    1000	 117427971 ns/op	  84.91 MB/s
BenchmarkDecompression-4         	    5000	  23340524 ns/op	 427.18 MB/s
	zstd_test.go:156: Reduced from 9970564 to 3444121

ᐅ git checkout 8ec87b6
~/datadog/zstd (8ec87b6) ᐅ GODEBUG=cgocheck=0 go test -run no_test -bench .
BenchmarkStreamCompression-4     	      10	 131603981 ns/op	  75.76 MB/s
BenchmarkStreamDecompression-4   	      50	  33397258 ns/op	 298.54 MB/s
BenchmarkCompression-4           	      10	 116480682 ns/op	  85.60 MB/s
BenchmarkDecompression-4         	      50	  22810589 ns/op	 437.10 MB/s
	zstd_test.go:156: Reduced from 9970564 to 3444121

[Viq111]

Closing in favor of #12.
We can cherry-pick 8ec87b6 when we will want to use the new streaming interface