Add newlines to the JSON stream functions

This makes the JSON streams a _lot_ easier to parse in less well-baked JSON parsers, and no less so in better ones.

Line-based JSON streams are very, very common, where simply chunk-based is not very common at all.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
registry: Added simple checksums (sha256) for layers

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam@docker.com> (github: samalba)
registry: Fixed tests

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam@docker.com> (github: samalba)
registry: Removed checksumPayload from exported fields

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam@docker.com> (github: samalba)
Rewrite docker rmi

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
bump API version

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
:= / var

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
fix tests

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
fix message 'No such image: ubuntu' => 'No such image: ubuntu:latest'

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
fix doc

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
fix bad rebase

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
add missing doc

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
add version pkg

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
registry: Fixed unexported field

Docker-DCO-1.1-Signed-off-by: Sam Alba <sam.alba@gmail.com> (github: samalba)
Fix exit code issue with TTY mode

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Fix TestCmdKill by closing the pipe before waiting on the container

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Merge pull request #4078 from vieux/rewrite_rmi

Rewrite docker rmi
Merge pull request #4357 from creack/fix_TestCmdKill

Fix TestCmdKill by closing the pipe before waiting on the container
Merge pull request #4346 from creack/fix_race_exit_code

Fix exit code issue with TTY mode
Fixed typo in Dockerfile example

Docker-DCO-1.1-Signed-off-by: Rob Cannon <rpcann@gmail.com> (github: robpc)

The 'true' command is located in /bin not /usr/bin in the busybox image.