isolate parts needed for cellpy-core #334
Description
The goal is to provide a slim cellpy-core version of cellpy that only performs the basic operations.
- receive data in a (not yet decided) specified format
- perform generation of a frame-agnostic step table
- perform summary statistics (frame-agnostic, unit-agnostic)
Since the 'full' cellpy package should reuse much of the code from the current version, it makes sense to start to try to distil out a 'core' from the current version (into another module) and make sure the 'current' cellpy works with that core.