Clarifying some language standards for the docs
[#3149] Tweaks thanks to @WouterJ
[#3149] Tweaking language to use a standard for capitalization
[Reference][Validation Constraints] Remove invalid default option markers and fix messages
Add cookbook entry about url trailing slash redirect
typo fixed
Merge pull request #3178 from bicpi/fix_validation_constraints_reference

[Reference][Constraints] Remove invalid default option markers; fix messages
add clarification for order in which event listeners will be executed

Clearing up ambiguity (are event listeners executed in priority or number order?).
[#3181] Adding line break thanks to @WouterJ
Merge pull request #3180 from EmmanuelVella/redirect-trailing-slash

Add cookbook entry about url trailing slash redirect
[#3180] Minor tweaks after proofreading new trailing slash entry
Update parameters.rst
Merge pull request #3187 from peterkokot/patch-6

Typo fixed
Merge pull request #3149 from symfony/language-standards

Clarifying some language standards for the docs
[#3134] Trying to clarify the purpose of the nonce logic
Bootstrapped the bootstrap Translation documentation
Added 'constructing the translator'
Moved framework indepent stuff to component docs
Rewrote component article
Rewrote book article