Add support for pathlib-based paths about chameleon

[malthe]

This is a good idea – I suppose it might be nice to use this as an excuse to add type specs to the main interfaces.

[markkuleinio]

Yeah and to be extra clear for other readers, I'm suggesting accepting both str and pathlib.Path (in type hint something like Union[str, pathlib.Path]).

[malthe]

@markkuleinio note that search_path must be an iterable, e.g. search_path=[my_path1, my_path2].

Ideally there would be some type-checking, but this is old-school Python and we haven't gotten around to adding any typings and there's not a lot of arguments checking either.