release 3.1

[kamilsk]

• [x] remove 2.2.x support
• [x] replace by $ composer require kamilsk/common:~3.1
• [x] add branch 4.x and add information about its supporting

               4.x------     - bc, 100% code quality and code coverage, php 7.0 only
             /           \
         3.x              \  - bug fixing, php 7.0 only
       /                   \
master --------------------- - porting new features from 4.x, php 5.6 and later