Add s2 commandline tools

[klauspost]

Commandline tools

Some very simply commandline tools are provided; s2c for compression and s2d for decompression.

Installing then requires Go to be installed. To install them, use:

go install github.com/klauspost/compress/s2/cmd/s2c && go install github.com/klauspost/compress/s2/cmd/s2d

To build binaries to the current folder use:

go build github.com/klauspost/compress/s2/cmd/s2c && go build github.com/klauspost/compress/s2/cmd/s2d

s2c

Usage: s2c [options] file1 file2
Compresses all files supplied as input separately. 
Output files are written as 'filename.ext.s2'.
By default output files will be overwritten.
Use - as the only file name to read from stdin and write to stdout.
Wildcards are accepted: testdir/*.txt will compress all files in testdir ending with .txt
Directories can be wildcards as well. testdir/*/*.txt will match testdir/subdir/b.txt
Options:
  -blocksize string
        Max  block size. Examples: 64K, 256K, 1M, 4M. Must be power of two and <= 4MB (default "1M")
  -c    Write all output to stdout. Multiple input files will be concatenated.
  -cpu int
        Compress using this amount of threads (default Auto)
  -faster
        Compress faster, but with a minor compression loss
  -help
        Display help
  -pad string
        Pad size to a multiple of this value, Examples: 64K, 256K, 1M, 4M, etc (default "1")
  -safe
        Do not overwrite output files

s2d

Usage: s2d [options] file1 file2
Decompresses all files supplied as input. Input files must end with '.s2' or '.snappy'.
Output file names have the extension removed. By default output files will be overwritten.
Use - as the only file name to read from stdin and write to stdout.
Wildcards are accepted: testdir/*.txt will compress all files in testdir ending with .txt
Directories can be wildcards as well. testdir/*/*.txt will match testdir/subdir/b.txt
Options:
  -c    Write all output to stdout. Multiple input files will be concatenated.
  -help
        Display help
  -safe
        Do not overwrite output files