Update performance documentation.

[ShaneHarvey]

The "performance" section in the documentation has not been updated since April 2014. Running the benchmarks today with go 1.7 and 1.8, it seems this library is slower than the stdlib in all but one benchmark (BenchmarkSHA256Large_*):

Go 1.8:

$ go version
go version go1.8.1 darwin/amd64
$ go test -bench=. -ldflags=-s
# github.com/spacemonkeygo/openssl
ld: warning: directory not found for option '-L/usr/local/opt/openssl@1.1/lib'
# github.com/spacemonkeygo/openssl
ld: warning: directory not found for option '-L/usr/local/opt/openssl@1.1/lib'
BenchmarkSHA256HMAC-4                     2000000           979 ns/op
BenchmarkSHA1Large_openssl-4                 2000       1161567 ns/op     902.72 MB/s
BenchmarkSHA1Large_stdlib-4                  1000       1125683 ns/op     931.50 MB/s
BenchmarkSHA1Small_openssl-4              1000000          1774 ns/op       0.56 MB/s
BenchmarkSHA1Small_stdlib-4              10000000           206 ns/op       4.85 MB/s
BenchmarkSHA256Large_openssl-4                500       2560554 ns/op     409.51 MB/s
BenchmarkSHA256Large_stdlib-4                 500       2934527 ns/op     357.32 MB/s
BenchmarkSHA256Small_openssl-4             500000          2017 ns/op       0.50 MB/s
BenchmarkSHA256Small_stdlib-4             5000000           286 ns/op       3.49 MB/s
BenchmarkStdlibThroughput-4                200000          7676 ns/op     133.40 MB/s
BenchmarkOpenSSLThroughput-4                50000         32563 ns/op      31.45 MB/s
BenchmarkStdlibOpenSSLThroughput-4         200000          8320 ns/op     123.07 MB/s
BenchmarkOpenSSLStdlibThroughput-4         300000          5981 ns/op     171.19 MB/s
PASS
ok      github.com/spacemonkeygo/openssl    104.153s

Go 1.7:

$ go version
go version go1.7.5 darwin/amd64
$ go test -bench=. -ldflags=-s
# github.com/spacemonkeygo/openssl
ld: warning: directory not found for option '-L/usr/local/opt/openssl@1.1/lib'
# github.com/spacemonkeygo/openssl
ld: warning: directory not found for option '-L/usr/local/opt/openssl@1.1/lib'
BenchmarkSHA256HMAC-4                     1000000          1352 ns/op
BenchmarkSHA1Large_openssl-4                 2000       1251402 ns/op     837.92 MB/s
BenchmarkSHA1Large_stdlib-4                  2000       1101072 ns/op     952.32 MB/s
BenchmarkSHA1Small_openssl-4               500000          2579 ns/op       0.39 MB/s
BenchmarkSHA1Small_stdlib-4              10000000           202 ns/op       4.93 MB/s
BenchmarkSHA256Large_openssl-4                500       2456446 ns/op     426.87 MB/s
BenchmarkSHA256Large_stdlib-4                 500       2891912 ns/op     362.59 MB/s
BenchmarkSHA256Small_openssl-4             500000          2962 ns/op       0.34 MB/s
BenchmarkSHA256Small_stdlib-4             5000000           277 ns/op       3.60 MB/s
BenchmarkStdlibThroughput-4                200000          6965 ns/op     147.01 MB/s
BenchmarkOpenSSLThroughput-4                50000         33866 ns/op      30.24 MB/s
BenchmarkStdlibOpenSSLThroughput-4         200000          6940 ns/op     147.53 MB/s
BenchmarkOpenSSLStdlibThroughput-4         200000          6994 ns/op     146.40 MB/s
PASS
ok      github.com/spacemonkeygo/openssl    97.231s

[superchalupa]

Unless you run on ARM: On ARM 32-bit, spacemonkey is 10x faster than stdlib for my server.