improve alpha sort in mflag

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Clarify how to update the docs branch in the RELEASE-CHECKLIST with concrete instructions

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
handle capital

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge auth package within registry

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Move signal to pkg

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Create portable signalMap

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Make docker use the signal pkg with strings

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Merge pull request #4515 from vieux/improve_sort_flags

improve alpha sort in mflag
Merge pull request #4567 from creack/merge_auth_registry

Merge auth package within registry
Merge pull request #4520 from tianon/clarify-docs-branch-update

Clarify how to update the docs branch in the RELEASE-CHECKLIST with concrete instructions
Merge pull request #4563 from creack/signal-improvment

Signal improvments