v1.19.1

• Fix invalid header name breaking the Guzzle middleware with recent guzzle/psr7
• Modify subprofile ID generator so that it's only ever composed of alphanumerics

v1.19.0

• Add Symfony HttpClient bridge
• Fix compatibility with PHP 5.3
• Fix sub-profile id generation to be compatible with url encoding

v1.18.0

• Deprecate methods and classes related to references