Bugfix/coords not deep copy

[pletchm]

This pull request fixes a bug that prevented making a complete deep copy of a DataArray or Dataset, because the coords weren't being deep copied. It took a small fix in the IndexVariable.copy method. This method now allows both deep and shallow copies of coords to be made.

This pull request corresponds to this issue #1463.

• Tests added
• Fully documented, including whats-new.rst for all changes and api.rst for new API

[pep8speaks]

Hello @pletchm! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-04-30 01:17:27 UTC

[pletchm]

I'm perplexed by why the build and tests are failing on this. I'm going to try 3 things:

1. Make a new branch from master and PR (making sure my fork master is synced up with the upstream master) to see if the tests/build pass without any additional commits
2. Commit my non-test changes and see if the build/tests pass
3. Commit my tests and see if the build/tests pass
   Then I'll rebase my 2 commits into 1 commit.

[mgaspary]

seems like the same issue again:

import xarray as xr

xarr1 = xr.DataArray(
    np.zeros([2]), 
    coords=dict(x=[0.0, 1.0]), # important to use 'float' here! with 'int' it is working fine
    dims=("x")
)
print(xarr1.x.data[0]) # 0.0

xarr2 = xarr1.copy(deep=True)
xarr2.x.data[0] = 45
print(xarr1.x.data[0]) # gives 45