Support pandas 1.0

[khaeru]

Pandas 1.0 is released. This PR makes one adjustment necessary to support pandas 1.0 in ixmp.

Details

The following tests failed:

• test_reporting.test_reporting_aggregate
• test_reporting_utils.TestQuantity.test_assert

The following tests trigger a segfault with pandas 1.0:

• test_reporting.test_reporter_add_product
• test_reporting.test_reporter_from_dantzig
• test_reporting.test_reporting_units
• test_reporting.test_report_size
• test_reporting.test_reporting_filters

The common cause seems to be a call to pd.Series.to_series() in reporting.utils.AttrSeries.__init__(); the former was removed in pandas 1.0. When the resulting AttributeError occured inside some new, C- or other compiled code in pandas, it triggered the segfault.

Supersedes #261, fixing CI errors on AppVeyor.

PR checklist

• Tests added. N/A
• Documentation added. N/A
• Release notes updated.

[khaeru]

Tests appear to pass as of 82561be.

[codecov]

Codecov Report

Merging #263 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #263   +/-   ##
=======================================
  Coverage   93.91%   93.92%           
=======================================
  Files          18       18           
  Lines        2037     2040    +3     
=======================================
+ Hits         1913     1916    +3     
  Misses        124      124           

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[zikolach]

Thanks @khaeru for fixing it quickly!