enhanced_http 3.0.0

A wrapper around the dart http package by provided by Google which is inspired by axios

3.0.0

• Added support for creating multiple instances
• Added http patch and http head method support
• Added support for providing headers at method level
• Added dart API documentation
• Updated the path parameter of request methods from a named parameter to a positional parameter
• Removed the onSuccess and onError parameters in favor of a single interceptors parameter which is available at both instance and method level
• Removed the formData parameter. A request is now considered as multipart/form-data based on the request header itself
• Refactored library code into separate files