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	Implemented in 2.1. Supported in 2.0 as consumer via extension.
4	Autoloading	2.0 uses PSR-4 compatible autoloader. 2.1 uses Composer autoloader.
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	Implemented in 2.1.
8	Huggable	It was a joke. Won't be adopted.
9	Security Advisories
10	Security Reporting
11	Container	#14112
12	Code style	Plan is to finish the standard and then follow it. Partially adopted.
13	Hypermedia Links
14	Events	#11389, #14349 NOTE: PSR-14 is going to be radically changed soon. Do not implement.
15	HTTP Middlewares	#15294
16	Cache	Implemented in 2.1.
17	HTTP Factories