Improved formatting (PSR standards)
    - Add "\" to curl-constants (to avoid conflicts in namespaced code)
    - Add "\" in doc-blocks
Constructor improvement:
    - Enable passing url as only argument, using parse_url to extract the data

Add exceptions in case bad/invalid/incomplete arguments were passed.
Add public access modifier to constructor
Change properties from private to protected
Fix bug in constructor (by adding a return statement)