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

Change PHPDoc return type of values() (myclabs#37)

To improve IDE autocompletion on the resulting items when iterating

Merge pull request myclabs#21 from lorenzomar/master

Change calls to method toArray() from self::toArray() to static::toArray()

Merge pull request myclabs#19 from chriseskow/values

Add static values() method to return array of all Enum instances (fixes myclabs#18)