MAINT: added pyproject.toml file

[aburrell]

Description

Fixes #118 by adding a pyproject.toml file.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Ran: pip install -e . from the ocbpy home directory.

Test Configuration

• Operating system: OS X Big Sur
• Version number: Python 3.9
• Any details about your local setup that are relevant: develop pysat, main ssj_auroral_boundaries

Checklist:

• Make sure you are merging into the develop (not main) branch
• My commits are formatted appropriately (following the SciPy/NumPy style)
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to Changelog.rst, summarising the changes
• Add yourself to AUTHORS.rst and .zenodo.json

[coveralls]

Coverage: 99.089%. Remained the same when pulling fd36e6a on pyproject_toml into 0f06156 on develop.