Merge branch 'master' into graph-tests

Author: MaximilianAlgehed

README.md

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 # constrained-generators
+[![Coverage Status](https://coveralls.io/repos/github/input-output-hk/constrained-generators/badge.svg?branch=master)](https://coveralls.io/github/input-output-hk/constrained-generators?branch=master)
+
 Framework for generating constrained random data using a subset of first order logic