Update documentation noting that SIGCHLD is not proxied.

Docker's --sig-proxy option sends all signals but one to a container. The
exception s SIGCHLD, which is deliberately ignored as it doesn't make sense to
send such a signal to a process in a container. Documentation updates will make
this less confusing if anyone does attempt to do this.

Docker-DCO-1.1-Signed-off-by: Matt Heon <mheon@redhat.com> (github: mheon)
add Docker version and branch to html header

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Fixed manpage generation script and README

Update md2man script to generate manpages inside docs/man/ directory. Update
usage documentation in the readme to point to the new docs/man path. Update
Ubuntu makefile to use new path to manpages

Docker-DCO-1.1-Signed-off-by: Matthew Heon <mheon@redhat.com> (github: mheon)
sort flags with the same name in a consistent order

Docker-DCO-1.1-Signed-off-by: Jonathan Boulle <jonathanboulle@gmail.com> (github: jonboulle)
Document memory limit sizing in manpages

The -m flag permits the setting of a memory limit when running a Docker
container. The actual limit set must be a multiple of page size on Linux, so
whatever number the uses passes in will be rounded up if needed. Document this
behavior to prevent confusion. Also fixed several small formatting and grammar
issues in the docker run manpage.

Docker-DCO-1.1-Signed-off-by: Matthew Heon <mheon@redhat.com> (github: mheon)
Update dockerimages.md

fix typo
Changed add to group command to include -a (append) flag, for safety. In response to customer email.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
allow overwrite in untar

Docker-DCO-1.1-Signed-off-by: Tibor Vass <teabee89@gmail.com> (github: tiborvass)
Merge pull request #6740 from tiborvass/untar_allow_overwrite

Allow overwrite in archive.Untar
Merge pull request #6678 from mheon/fix_man_generate

Path fixes in md2man script and README
Merge pull request #6731 from mchelen/patch-2

Update dockerimages.md
Merge pull request #6680 from mheon/cgroup_memory

Update docker-run manpage
Merge pull request #6713 from vieux/order_flag

sort flags with the same name in a consistent order
Merge pull request #6741 from fredlf/suse-install-fix

Changed add to group command to include -a (append) flag, for safety. In...
missing `sudo`
fix typo
Merge pull request #6751 from mchelen/patch-3

missing `sudo`
Merge pull request #6752 from mchelen/patch-5

fix typo
added linkage to tugboat, a scala client

Docker-DCO-1.1-Signed-off-by: Doug Tangren <d.tangren@gmail.com> (github: softprops)
Merge pull request #6747 from softprops/master

added linkage to tugboat, a scala client library