Added class to manage URLs
Added interface for http request senders.
Added default values for arguments.

setHeaders and setParameters now accept null arguments to empty the headers and parameters.
require Applistic\Common to help with the key/value properties.
Replaced headers and parameters properties (arrays) by Applistic\Common\KeyValue objects
Moved the code building a query string to a static function for external access
Removed  for property accessor. Only the property name should be required.
Added a function that accepts a request object to send.
Added abstract sender and first sender using curl