Added new type-safe API that allows validating a given value against a given `class-string<Enum>`#143

Ocramius wants to merge 5 commits intomyclabs:mastermyclabs/php-enum:masterfrom

Ocramius:fix/static-analysis-of-enum-from-method-fixOcramius/php-enum-1:fix/static-analysis-of-enum-from-method-fixCopy head branch name to clipboard