PSR adoption

The table below indicates PSRs usage in Yii framework.

PSR	Purpose	Status
0	Autoloading	Deprecated standard.
1	Code Style	Partially adopted.
2	Code Style	Partially adopted.
3	Logger	Supported as consumer via extension. Mentioned in logging guide. See #13641, #13706, #13702. Work in progress for 2.1 in #14611.
4	Autoloading	Supported.
5	PHPDoc	Plan is to finish the standard and then follow it. Partially supported. We're writing phpdoc according to support in PhpStorm and NetBeans IDEs. #11635
6	Cache	Won't be adopted. See PSR-16.
7	HTTP Message	#13763, #10824, #10833, #11328
8	Huggable	It was a joke. Won't be adopted.
9	Security Advisories
10	Security Reporting
11	Container
12	Code style	Plan is to finish the standard and then follow it. Partially adopted.
13	Hypermedia Links
14	Events	#11389, #14349
15	HTTP Middlewares
16	Cache	Supported in 2.1.
17	HTTP Factories