Bootstrapped the bootstrap Translation documentation
Added 'constructing the translator'
Moved framework indepent stuff to component docs
Rewrote component article
Rewrote book article
Moved cookbook article
Moved basic usage to its own article
updated new article
Added index directive
Reread component docs
Reread usage docs
Reread book article
Fixed things mentioned by the great @xabbuh
Added new 2.2 features
Fixes
[#2906] Final massive proofread of the translation book-component split

Some things that were moved to the components were moved back in part to the book so that it still feels complete.

I also took this opportunity to tweak some things to make them more understandable.
Merge pull request #3190 from symfony/WouterJ-document_translation_22

Wouter j document translation 22