v0.21.0

Features

• add TypeScript types (#189) (76cfef8)

BREAKING CHANGES

• is-class is not longer used, use instanceof instead

The DAGNode.isDAGNode() and DAGLink.isDAGLink() methods no longer exist,
use instanceof DAGNode and instanceof DAGLink instead.

Please note that the newly added TypeScript types might lead to warnings/errors
if you use it in a TypeScript types checking environment.