Tries to clearify redirecting article
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
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
[Cookbook][Forms] Add Asterisk alternative using CSS
Remove confusing sample code
Use sidebar; improve text
[reference] fixed wrong class reference in form/types/locale.rst
Tried to clarify #3255
Merge pull request #3243 from xabbuh/fix-build-errors

Fix build errors
Replace gendered pronouns with gender-neutral

For consistency sake, instances of "he", "she", "his", "hers",
"his/hers", "he/she", etc were replaced with "they", "their", etc (or
were removed all together in cases where they weren't necessary). Verb
tenses should also have been corrected where changes were made.
Merge pull request #3245 from bicpi/fix_front_controller_code

[Cookbook][Configuration] Fix front controller sample codes
[#3245] Removing most of the front controller code altogether

This removes code that could easily become out of date again. Also, I don't think
it was necessary - we want to focus them on only one line anyways.