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Add compatibility of sphinx conversion with ipywidgets. Note, the sphinx version dependency is now >=1.8.

Additionally, the code base has been formatted by black, and some minor bugs/warnings have been fixed.

• Ensure equations that are already wrapped in a math environment are not wrapped twice.
• For RST output, ensure multiline equations are correctly indented

Up-date the Conda requirements to working versions

Changes include:

• implement HTML2JSONParser and pytest-regressions for testing HTML documents

Rather then searching for specific bits of text, we convert the document to a json object, stripping out sections irrelevant for testing (like the header, footer and scripts that can change between versions). and test with the data_regression fixture

• Add pre_commit configuration
• Update .travis.yml to test python 3.7 rather than 3.4 (which is deprecated)
• Update RTD configuration
• version bump

• remove sphinx.ext.imgconverter from sphinx auto-builds
• add additional known sphinx roles