Fix Path deepcopy signature

[has2k1]

Problem

Path.__deepcopy__ does not accept a second(memo) parameter,
so the common usage of the deepcopy function fails.

Solution

Add second parameter.

[dopplershift]

👍 For anyone else wanting more information on __deepcopy__ see: https://docs.python.org/3.5/library/copy.html?highlight=__deepcopy__

I don't think any of the tests failures were related--I restarted the failing Travis jobs to confirm. Can someone restart the AppVeyor job?

[tacaswell]

https://docs.python.org/3.5/library/copy.html?highlight=__deepcopy__ <- fixed the link for you 👿

Do we need to do anything with memo?

[has2k1]

memo is to deal any circular stuff. Since the class is offloads the copying of the relevant structures to numpy, then memo can be safely ignored.

However, hold on this until I can fix another issue with the copy. I am not in position to do so at the moment.

[dopplershift]

@tacaswell What link problem? 😁 I blame Google/Python defaulting to 2.x on the docs when I search.

[has2k1]

Okay. I fixed the other issue of not being able to deecopy if the path had no codes.

[tacaswell]

Backported to v2.x as b338a71

@has2k1 Thanks!