v0.17.0: Release 0.17.0

Features:
- stagpy is now fully type annotated and statically checked with mypy.
  Several typing bugs were solved in the process.
- new velocity, acceleration and heat_production scales
- new field_header and field_istep parsers, the legacy fields parser API
  is simplified accordingly
- filters over _StepsView now compose instead of superceding each other
- ParsingErrors are now raised when parsing ill-formed xdmf files
- NoGeomError is raised when no geometry information is available for
  a Step
- NoRefstateError is raised when refstate cannot be found
- NoTimeError is raised when step.time cannot be found
- field.plot_iso can take a field argument to plot instead of the
  requested field, akin to field.plot_scalar

Improvements:
- NamedTuples are used instead of the older API namedtuple
- processing.stream_function returns a Field instead of an array
- processing.*_rprof returns Rprof instances instead of arrays
- time series processing functions return Tseries instead of arrays

Compatibility:
- drop Python 3.6 support, add 3.10
- bump several dependencies versions

Fixes:
- _Scales.length takes air thickness into account
- interpolate vector fields to cell centers in plot_scalar
- no longer use deprecated options of pandas.read_csv

Internals:
- use tox4 and tox-gh for CI
- use setup.cfg instead of setup.py, remove MANIFEST.in