Issue cleanup for 2.0.0 release, part 1

[kandersolar]

• Code changes are covered by tests
• New functions added to __init__.py no new functions
• API.rst is up to date, along with other sphinx docs pages
• Example notebooks are rerun and differences in results scrutinized
• Updated changelog

Old issue cleanup for 2.0.0. This addresses #191, #114, and #198.

For #114, I tested each pandas release from 0.23.2 to 1.0.0 and the only one with the issue was 0.24.0. Rather than bump the minimum version, I just excluded that specific version.

The complexity of the deprecation machinery is worth it IMHO -- it automatically modifies docstrings with a deprecation message, which then shows up in IDEs as well as propagating to the sphinx docs:

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[mdeceglie]

LGTM!