lxc: Allow set_file_cap capability in container

This means you're able to set the bits for capabilities on files
inside the container. This is needed for e.g. many fedora packages
as they use finegrained capabilities rather than setuid binaries.

This is safe as we're not adding capabilities really, since the
container is already allowed to create setuid binaries. Setuid
binaries are strictly more powerful that any capabilities (as root implies
all capabilities).

This doesn't mean the container can *gain* capabilities that it
doesn't already have though. The actual set of caps are strictly
decreasing.
Configured FPM to make /etc/init/docker.conf a config file.
Hint for Remote API doc details in header links
Used tabs for alignment when I should've used spaces. Fixed.
Clearly point at detailed docs
Update archlinux.rst

The /etc/sysctl.conf file is deprecated
https://www.archlinux.org/news/deprecation-of-etcsysctlconf/
Update archlinux.rst
Fix Ping endpoint documentation
Add/modified the canonical link to work with all /index/ links. Added style for "danger'
Cleanup
Bump vendor kr/pty to commit 3b1f6487b (syscall.O_NOCTTY)
Merge pull request #2047 from Thermionix/patch-1

Update archlinux.rst
fix(hack/PACKAGERS): add xz utils as a runtime dep
Merge pull request #2014 from alexlarsson/allow_set_file_cap

* Runtime: lxc: Allow set_file_cap capability in container
Merge pull request #2066 from tianon/vendor-bump-kr-pty

Bump vendor kr/pty to commit 3b1f6487b (syscall.O_NOCTTY)
Remove Gentoo install notes about #1422 workaround
Update ubuntu docs to use wget instead of curl

Ubuntu doesn't come with curl.

wget instead of curl

nicer wget syntax

remove /dev/null
Merge pull request #2065 from kyleconroy/fix_ping_endpoint

Fix Ping endpoint documentation
Merge pull request #2073 from tianon/gentoo-no-more-1422-hack

Remove Gentoo install notes about #1422 workaround
Merge pull request #2063 from dhrp/doc-template-fix

Doc template fix