REL: 0.8.2

This is the first bug-fix release of datrie to make compatible with
Python 3.8.  There should be no change in behavior from 0.8

* Future-proof Python support by making cython a build time dependency and
  removing cython generated c files from the repo (and sdist).
* Fix collections.abc.MutableMapping import
* CI and test updates
* Adjust internal library name to unbreak some linkers