Merge pull request myclabs#84 from KartaviK/hotfix/ext-json-requirements

 Add ext-json to requirements for package

Merge pull request myclabs#83 from KartaviK/feature/envelope-enum-con…

…struct

 Create instance of enum from same enum in constructor

Merge pull request myclabs#82 from myclabs/fix-coding-style

Fix coding style

Merge pull request myclabs#78 from KartaviK/feature/nullable

Set opportunity to create enum statically with null value

Merge pull request myclabs#75 from willemstuursma/php-72-optimizations

Prefix all function calls with a backspace

Merge pull request myclabs#71 from osavchenko/allow_null_in_equals

allow null in equals

Merge pull request myclabs#63 from myclabs/mnapoli-patch-1

Recommend using private constants

Merge pull request myclabs#56 from remicollet/issue-phpunit

Use modern phpunit

Merge pull request myclabs#48 from peter-gribanov/equals-fix

Fix method equals is incorrect working

Move installation instructions at the top of the README