* improve links
 * add gathered information about upstream for some items
 * fix formatting

/reviewed-on nexedi/slapos!358

It is application/json no text/json.

Cf !358 (comment 63538)

Desipte of original analysis the middleware plugin is not needed, as Caddy's
http.rewrite + http.proxy is powerful enough to set headers depending on the
header regular expression.

This will ease further development

In those places caddy_custom_https (and it's backward compatbility companion
apache_custom_https) was not checked, thus making it impossible to just use
https customisation, without http one.

caddy_custom_http and caddy_custom_https are implemented and exposed
instead of apache_custom_http and apache_custom_https, but with backward
compatbility for the latter form from apache-frontend.

In TODO mark missing usage of custom http found during work on this commit.

Required by e.g. tcpu.py:

	kirr/neo@a60c472c

Reported by Julien

The feature is postponed and noted in TODO.

The `gzip` declaration uses defaults, which seems reasonable.

/reviewed-on !352

The md5sum was not updated, so update it ASAP.

In case of error during processing SlapOS software or instance expose
last 100 lines of the message, which is enough to identify the problem and
does not clutter the test master.

@vincentB @kazuhiko 

/reviewed-on nexedi/slapos!351

/reviewed-on nexedi/slapos!350

Commit c6c919dc (Remove all occurrences of the obsolete
'parameters-extra' option) removed

	parameters-extra = true

because after 5c980caf (Drop the 'parameters-extra' option and always
forward extra parameters) "$@" is always implicitly added to argv.

Clarify the comment that was explaining what `parameters-extra = true`
was doing, since it was not updated during parameters-extra removal.

Features:

 * amend configuration with comments
 * drop obsolete comments from Apache copy
 * remove not needed whitespaces
 * use indentation for conditionals in Jinja2

Where applicable simplify Jinja2 templates by removing Caddy-TODO
and fill or update TODO.rst.