Features
* Add ``pinttr.field()`` ({ghcommit}`992acf`).
* ``pinttr.ib()``: Add nicer default repr ({ghcommit}`d68ec4`).
Developer-side changes
* Automate testing with GitHub actions ({ghcommit}`1997a7`).
* Manage changelog with Towncrier ({ghcommit}`644ecc`).
* Add coverage report with Codecov ({ghcommit}`fa658d`).