add pyproject.toml to ensure pip builds have Cython and numpy

[dmeliza]

pip install pyspike will often fail if Cython is not already in the environment because the C-code stored in the source tree may not work with newer versions of python. Adding a pyproject.toml file will enable the new PEP517 build system, which can ensure particular packages are present during building.

[dmeliza]

Bumping this pull request to see if it can be merged. We are using poetry to manage dependencies and so we currently have to build our own wheels to use pyspike.