Implement PATCH request

Closes easybib/issues#831

To be tagged 0.5.0

## Warning: breaking change

This is a **breaking change** for existing new implementation in project-folders, because of [this delta](https://github.com/easybiblabs/api-client-php/pull/10/files#diff-c70312336f5e6fe1ebbfea2670f7fa14L119)