added function torusW

[MgeeeeK]

1. You have run tests on this submission, either by using Travis Continuous Integration testing testing or running nosetests on your changes?
2. This pull request is directed to the pysal/master branch.
3. This pull introduces new functionality covered by
   docstrings and
   unittests?
4. You have assigned a
   reviewer and added relevant labels
5. The justification for this PR is: Added an argument torus and its functionality in function lat2w, this fixes the issue pysal/pysal#894

[sjsrey]

Please add a test for integration and to document expected behaviour.

You can add a test in https://github.com/pysal/libpysal/tree/master/libpysal/weights/tests

See other tests in that directory for examples. Let us know if you have questions after that.

[MgeeeeK]

Please add a test for integration and to document expected behaviour.

I've added a test for the function lat2W(torus=True)

[MgeeeeK]

@sjsrey should i instead create a new function for torus just like hexLat2W?

[sjsrey]

@MgeeeeK I think separating this out to its own function, maybe torusW would be a good way to modularlize things.

[AppVeyorBot]

✅ Build libpysal 1.0.25 completed (commit c6a3ba2101 by @sjsrey)

[codecov]

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[AppVeyorBot]

✅ Build libpysal 1.0.29 completed (commit 73d5f7a62d by @MgeeeeK)

[MgeeeeK]

@sjsrey new commits contains:

1. separate function for torus called torusW
2. unittests for torusW and hexLat2W
3. fixes for lat2SW (it gave error when (ncols = 1, criterion = "rook") and (ncols = 2, criterion = "queen")

sorry for reopening this pr...i messed up my dev environment earlier so had to drop all my commits.