Sort out documentation of params (`base_url` etc)

[arildm]

Parameters of the Matomo class are documented to various extents in three places. It is difficult to know what options there are, and where to look for more information about them. The base_url parameter is actually not documented at all.

• Docstring in core.py
• README
• Getting Started: readthedocs.io, source
• Configuration: readthedocs.io, source

parameter	docstring	README	Getting Started	Configuration
matomo_url	X	X	X
id_site	X	X	X
token_auth	X	X	X
base_url	X
client
ignored_routes			X	X
routes_details		X	X	X
ignored_patterns	X		X	X
ignored_ua_patterns				X