Tries to clearify redirecting article
Update references to current branch

E.g. changed "2.2" to "2.3" and so on
Update overview.rst
use handleRequest() instead of bind()
Improvements to registering an extension (#2)

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #9644 (symfony) and #3231 (symfony-docs)

1. The original text is good but the topic of that paragraph is not "extension conventions" but "registering an extension" (i.e. if you follow these conventions then register goes like so ..)

2. Cleaned up different terminology "Conventions" v "Standards" -> just conventions now

3. Move this part to a more logical place. First create then register, then modify for additional needs.
Changed due to comments in repo collab
links in documentation overview contributing moved to bottom
Fixed namespace in Handling Form Submissions standalone example.
some tweaks for #3190
Merge pull request #3238 from peterkokot/patch-2

Links in documentation overview contributing moved to bottom
Merge pull request #3239 from zsjavorszky/fix_form_handling_example

Fixed namespace in Handling Form Submissions standalone example.
fix two little syntax errors
[Cookbook][Configuration] Fix front controller sample code
[Cookbook][Console] Fix statement
[Cookbook][Assetic] Update JS minifier recommendation
Fix formatting
Improve ISO code references
fixed markup
Update language field/constraint
Added sphinx files