Pyfk

This is the third release of the package, and has some excellent updates!!!

1. Now the package uses poetry as the package manager and no longer uses setup tools for installation. From now on we can use a more "modern" python packaging system with [pep 517](https://peps.python.org/pep-0517/). It also helps to resolve the dependency conflict.
2. Now the package supports any planets other than Earth by providing `r_planet` in `SeisModel` and `planet_radius` in `Config`. Note we have to provide them all at the moment, future versions might directly derive `planet_radius` from `r_planet`. The default values for them are 6371.
3. Now the noise suppression factor sigma has can be adjusted in `Config` (default to 2). It is hard to describe how to adjust this value, but the suggestion is that to use 2 first, and adjust it if there is too much numerical noise.

**Full Changelog**: https://github.com/ziyixi/pyfk/compare/v0.2.0...v0.3.0

This is the second public release of PyFK, and the features include:

1. Parallel mode in MPI
2. Parallel mode in CUDA
3. Ability to simulate the waveform on other planets (still have the bugs to fix, release on future versions)

This version is compatible with previous versions.

v0.2.0-beta.6.1
Let conda workflow only on Linux.

Use pyproject.yml to download the dependencies, as cysignal has a problem in downloading with easy_install.

This is the beta test version for PyFK. All the old API should be consistent, and there are several new features:
+ Support to use MPI
+ Support to run on GPU (with CUDA)
+ Updated document and tutorial (WIP)

After updating the document, and modifying several APIs (currently undocumented, set as the environment variables for the GPU mode), the v0.2.0 will be published.

This is the first public release of pyfk. And it mainly offers:

* some basic configuration classes
* the function to calculate the Green's function
* the function to convolve the Green's function with the source time function

And some utility functions:
* the function to generate a simple trapezoid source time function