Stockwell

- Make it possible again to directly call functions from submodules, like it
was in versions prior to v1.1. Example:

python
import stockwell
stockwell.st.st(data, fmin, fmax)

- Remove support for Python 3.6 and 3.7
- Add support for Python 3.11 and 3.12
- Support for Numpy 2.0!
- Added a script to download and compile FFTW3

- Use ctypes to wrap the modules written in C
- License changed to GPLv3

- Packages for Python 3.10 and macOS arm (M1, M2)

- Fix for missing file in source distribution

- New parameters for `st.st()`: `gamma` and `win_type`:
- `gamma` can be used to tune the time and frequency resolutions
of the S-transform.
- `win_type` can be set to 'gauss' (default) and 'kazemi' (Kazemi, 2014)