update RTD config scripts

[kafitzgerald]

Updated the Read The Docs configuration scripts and requirements.

Built the docs, but haven't tested the RTD build (is there a way to do this before merging?).

Updated to version 2.0 config and tried to use some of these tips to minimize build resources: https://docs.readthedocs.io/en/latest/guides/build-using-too-many-resources.html

[coveralls]

Pull Request Test Coverage Report for Build 538

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.188%

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Totals
Change from base Build 536:	0.0%
Covered Lines:	3733
Relevant Lines:	4233

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💛 - Coveralls