Split out from #369. See also https://github.com/johnkerl/miller/blob/master/go/README.md.

Pre-release/rough-draft docs are at http://johnkerl.org/miller6.

Things which may change:

As noted in go/README.md, I want to preserve as much user experience as possible. That said:

• --jvstack and --jsonx will still be supported as command-line flags, but JSON output will be pretty-printed (like --jvstack) by default.
• --csvlite will still be different from --csv, as detailed below.
• emitf and emitp were invented before I had for-loops in the DSL. If people really want to keep
  these and are using these, I can keep them; but maybe we're better off leaving them behind. Please
  let me know.
• CR vs CR/LF (line-endings) will be platform-appropriate using Go's own portability -- Windows files will be written correctly on Windows, and likewise for Linux and MacOS. That said, I don't know if we need any longer to preserve CR/LF-to-CR/LF even on Linux (line endings which are non-standard for the platform) -- again, please let me know.
• mlr put -S and mlr put -F will become unnecessary since string-conversion will be done just-in
  -time as suggested by @gromgit on [REQ] JIT numeric conversion in mlr put, part 2 of 2 #151.

Please include here any thoughts you have on the Go port.