BUG: Fix closing files manually

[snowman2]

In #606 it became evident that the files were not being closed. This fix should help users to close Datasets that have data_vars pointing to files.

• Related How to overwrite raster opened with rioxarray.open_rasterio ? #485
• Related can only read 32 layers from .hdf files before returning a FileNotFound error #544
• Fully documented, including docs/history.rst for all changes and docs/rioxarray.rst for new API

[codecov]

Codecov Report

Base: 96.33% // Head: 96.37% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (a85545d) compared to base (49f2815).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #607      +/-   ##
==========================================
+ Coverage   96.33%   96.37%   +0.04%     
==========================================
  Files          11       11              
  Lines        1691     1711      +20     
==========================================
+ Hits         1629     1649      +20     
  Misses         62       62              

Impacted Files	Coverage Δ
rioxarray/_io.py	96.55% <100.00%> (+0.10%)	⬆️
rioxarray/xarray_plugin.py	92.59% <100.00%> (+1.28%)	⬆️

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[snowman2]

Thanks @justingruca 👍