Deprecate py.path support

[WillAyd]

Since our min version is Py35 path lib is guaranteed to be installed. However we have a few functions that accept py.path.LocalPath objects for compatability

Not sure if we need an explicit deprecation cycle or if this is implied with moving minimum support to Py35

[jreback]

we should deprecate as have accepted these for a long time and they work py 3

[nandahkrishna]

If possible, I'd like to contribute to this. Should I search for functions with LocalPath and deprecate them accordingly?

[WillAyd]

@nandahkrishna that's great! And yes you've got it right. You might want to check out other PRs labeled Deprecate that have been merged to see how we typically handle as well

[nandahkrishna]

You might want to check out other PRs labeled Deprecate that have been merged to see how we typically handle as well

Sure, I'll do that. Thanks!

[nandahkrishna]

I took a look at previous PRs labeled deprecate. I got a fair idea of how it works, but I couldn't seem to find a case that deprecated an external library (might have missed my eye?) so just confirming:

1. Visit functions where py.path.local has been used
2. Add a DeprecateWarning with a suitable message
3. Add tests for the warning
   Is this right?

[WillAyd]

That's right!