Enhancement to the C client generator

Description

Below please find a list of pending enhancements to the C client generator:

• Change required cURL version to 7.58.0
• Fix authentication methods(either with a new #define or by only generating the correct code snippet)
• Allow multiple uses of the apiClient_t object
• Build as library
• Add build target "make install"
• Provide/Document an example how to use the generated code for a client
• Better Unit-Tests
• Better cURL/HTTP error code handling

openapi-generator version

Latest master

Related issues/PRs

#226 (closed) #516

Suggest a fix/enhancement

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