Merge pull request #2728 from imobilis/ticket_7884

[WCM] [Process] Doc for output flush methods.
[#2728] Minor tweaks to docs on Process flush methods
Merge pull request #2971 from xabbuh/issue-2958

document the getEncodings() method of the Request class
[#2971] Minor language tweak to be consistent with the other areas

The language used by @xabbuh is actually straight from the PHPDoc, which is cool, but I don't love
the wording there, and having some variety in wording might help clarification.
Merge pull request #2975 from xabbuh/issue-2973

Note about custom formats and the HTML5 date type
[#2975] Taking the talk about the HTML date field further by updating default values and tweaking related details
Merge pull request #2976 from michelsalib/patch-1

Fixing wrong parameter name in redirecting in config
Merge pull request #2981 from bicpi/remove_tip_for_validation_groups

[forms] Remove tip for skipping validation group section
Merge pull request #2982 from bicpi/fix_cookbook_dynamic_form_modfication_example

[cookbook/form/dynamic_form_modification] Fix sample code
Merge branch '2.0' into 2.1
Merge branch '2.1' into 2.2
Merge pull request #2984 from peterkokot/2.1

Update installation.rst
Merge branch '2.1' into 2.2
clarifies that resolve() does return a plain array of options
Merge pull request #2988 from iamdto/fix-config-prototype-code-sample

[Components][Config][Definition] Fix code sample
make the advantage and disadvantage of the ACL more clear

For me as a SF2 developer to handle data manipulation was pretty new to me. So I asked in the irc and searched the web and finally landed on this documentation page. So it looked like this is the way to go and it is a usual thing like using bundles in SF2. But it isnt, it is a far more complex permission handler which will work upfront and is not that much flexible.

I would highly recommend to add at least some notes, so that other developers getting a note on that and can maybe save some days of work as the opposite of me.
added xabbuh corrections
added stof´s corrections
[#2989] Moving the message about ACL alternatives higher up and furthering the message
[#2975] Removing duplicate note