Initial library creation tasks

[WarrenWeckesser]

This is a rough "to do" list. The tasks probably need to be refined.

• Get the financial functions from numpy into this repo., and create a basic package structure (setup.py, etc) that allows the package to be installed locally.
  - Done in #1
• Configure testing for running tests with pytest, and set up CI.
  - I set up a github workflow to run the tests with numpy >= 1.17 with Python versions 3.5, 3.6, 3.7 on ubuntu. That's enough to consider this task done. We can add more platforms later.
• Change setup.py and anything else necessary so the version is visible wherever it is needed: in setup.py, as numpy_financial.__version__, etc.
  - Done in bf4808c
• Set up documentation (Sphinx, etc.)
  - Documentation builds on each push to the master branch, and is available to view at https://numpy.org/numpy-financial/
• Upload package to PyPI; get feedback.
  - Version 0.1.0 was uploaded to PyPI on October 10, 2019.
• Release 1.0

After releasing 1.0, we can:

• Add deprecation warnings to the financial functions in NumPy.
• Transfer the open GitHub issues about the financial functions from the NumPy repo to this one.
• Freeze the NumPy financial library. Direct all future issues and pull requests to this repo.

[person142]

@WarrenWeckesser given that 1.0 has been released, it looks like everything in this issue has been done?

[WarrenWeckesser]

@person142, yes, thanks for the reminder!