ResourceIdentifier to allow multiple meta props (fixes json-api-php#99)…

… (json-api-php#100)

Relationship with no "data" member. Fixed json-api-php#92 (json-api-p…

…hp#93)

Update CHANGELOG.md (json-api-php#91)

v2 release (json-api-php#84)

Simplification, Formatting, Performance (json-api-php#83)

Update CHANGELOG.md (json-api-php#82)

Fix the link (json-api-php#79)

Update CHANGELOG.md (json-api-php#76)

Make exceptions more precise (json-api-php#72)

Update README (json-api-php#71)