Add __slots__ to MultiVector

Remove hopefully last outdated Blade references

Bump version to 1.2.1

Update PyPI classifiers

str() is now format(, '.2f')

docs: Remove duplicate mention of grade

Add format() support to control precision

Add blade tests for str() and repr()

Run tests on more Python versions

Put docs dependencies in a requirements file

Fix doctests

Finish Sphinx docs

Get started moving docs to Sphinx

Run tests with pytest

Bump version to 1.2.0