Docstring generation code moved to method __generate_init_docstring

The docstring autogeneration feature can be toggled using the global
flag 'docstring_signature'.

docstring_signature
Improved local variable names
Now updating the class docstring instead of the __init__ docstring
Now showing the parameter type instead of the default value
Class parameter signature now declared as Parameters(...)
Set docstring_signature to True by default
Deleted docstring for Parameterized.__init__

IPython tooltip was showing the docstring for Parameterized.__init__
when used on ParameterizedFunctions. Removing this docstring fixes this
issue and the class level docstring is shown as required.