Step towards v2

v1.6 (#421)

* version bump

* Added --ease-anticipate-* easings (#419)

* breaking change: added --ease-elastic-in, renamed --ease-elastic-* and --ease-squish-* to --ease-elastic-out-* and --ease-elastic-in-out-*

* Update docsite/index.css

Fixed typo from refactor in docsite/index.css as per Adam's comment

Co-authored-by: Adam Argyle <argyle@google.com>

* adjusted tests to correspond to additional props we added

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Co-authored-by: Alex Li <alex.li@twosigma.com>
Co-authored-by: Adam Argyle <argyle@google.com>

* document and create fallback

* update tests

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Co-authored-by: Alex Li <aml7hqv@virginia.edu>
Co-authored-by: Alex Li <alex.li@twosigma.com>