update dependencies and lint

Closes #47

See merge request !26

- use more reliable sympy API (closes #47)
- fix linter warnings except for long lines
- remove obsolete patch

generalize PointGroupElement input

Closes #7

See merge request !24

normalize scalar U to array, parse strings through sympy,
convert U to numpy array.

closes #7

Saving qsymm models

Closes #34

See merge request !23

fix python 3.9 support

See merge request !21

fix multiple warnings

See merge request !19

Anton Akhmerov authored 4 years ago and Dániel Varjas committed 4 years ago

- Use the undeprecaded sympy objects and imports
- Avoid potentially creating an array of arrays with different shape
- Properly use pytest.warns

Mitigate setuptools warning

See merge request !18

Since setuptools-49.2.0 importing distutils before setuptools started to
raise a warning. Moving importing _version.py to the top mitigates this
warning.

This is a decent integration test.
Closes #9.