DOC: Address issue where documentation is excluded due to a gitignore rule.

(cherry picked from commit fbc4e77321f6e92b7af658ce8257b6231c6ebac9)
DOC: indicate that weight zero is reported as DRAIN

It's not the same state but reported as such.
(cherry picked from commit c5af3a6d15358fa8b5be6151239862efde4c36f7)
[RELEASE] Released version 1.5.5

Released version 1.5.5 with the following main changes :
    - DOC: Address issue where documentation is excluded due to a gitignore rule.
    - MEDIUM: Improve signal handling in systemd wrapper.
    - BUG/MINOR: config: don't propagate process binding for dynamic use_backend
    - MINOR: Also accept SIGHUP/SIGTERM in systemd-wrapper
    - DOC: clearly state that the "show sess" output format is not fixed
    - MINOR: stats: fix minor typo fix in stats_dump_errors_to_buffer()
    - DOC: indicate in the doc that track-sc* can wait if data are missing
    - MEDIUM: http: enable header manipulation for 101 responses
    - BUG/MEDIUM: config: propagate frontend to backend process binding again.
    - MEDIUM: config: properly propagate process binding between proxies
    - MEDIUM: config: make the frontends automatically bind to the listeners' processes
    - MEDIUM: config: compute the exact bind-process before listener's maxaccept
    - MEDIUM: config: only warn if stats are attached to multi-process bind directives
    - MEDIUM: config: report it when tcp-request rules are misplaced
    - MINOR: config: detect the case where a tcp-request content rule has no inspect-delay
    - MEDIUM: systemd-wrapper: support multiple executable versions and names
    - BUG/MEDIUM: remove debugging code from systemd-wrapper
    - BUG/MEDIUM: http: adjust close mode when switching to backend
    - BUG/MINOR: config: don't propagate process binding on fatal errors.
    - BUG/MEDIUM: check: rule-less tcp-check must detect connect failures
    - BUG/MINOR: tcp-check: report the correct failed step in the status
    - DOC: indicate that weight zero is reported as DRAIN
BUG/MEDIUM: systemd: set KillMode to 'mixed'

By default systemd will send SIGTERM to all processes in the service's
control group. In our case, this includes the wrapper, the master
process and all worker processes.

Since commit c54bdd2a the wrapper actually catches SIGTERM and survives
to see the master process getting killed by systemd and regard this as
an error, placing the unit in a failed state during "systemctl stop".

Since the wrapper now handles SIGTERM by itself, we switch the kill mode
to 'mixed', which means that systemd will deliver the initial SIGTERM to
the wrapper only, and if the actual haproxy processes don't exit after a
given amount of time (default: 90s), a SIGKILL is sent to all remaining
processes in the control group. See systemd.kill(5) for more
information.

This should also be backported to 1.5.
(cherry picked from commit 74f016985ab1fa7a6a5afa301d982e77eba9c96a)
BUG/MEDIUM: config: avoid skipping disabled proxies

Paul Taylor and Bryan Talbot found that after commit 419ead8 ("MEDIUM:
config: compute the exact bind-process before listener's maxaccept"),
a backend marked "disabled" would cause the next backend to be skipped
and if it was the last one it would cause a segfault.

The reason is that the commit above changed the "while" loop for a "for"
loop but a "continue" statement still incrementing the current proxy was
left in the code for disabled proxies, causing the next one to be skipped
as well and the last one to try to dereference NULL when seeking ->next.

The quick workaround consists in not disabling backends, or adding an
empty dummy one after a disabled section.

This fix must be backported to 1.5.
(cherry picked from commit 06cc905813f1858c0606b44d1e271bd0b6a25224)