Pyxirr

- Wheels for python 3.10
- Add Rate, IPMT, PPMT ([18](https://github.com/Anexen/pyxirr/pull/18))
- Test against `numpy-financial` when possible

- XIRR improvements ([15](https://github.com/Anexen/pyxirr/pull/15))
- add more xirr tests
- handle XIRR close to -1
- fix nfv signature; always return None instead of nan

- Support Series with DatetimeIndex ([13](https://github.com/Anexen/pyxirr/pull/13))

- Add NFV, XFV, XNFV ([11](https://github.com/Anexen/pyxirr/pull/11))

- Add XFV, PMT, NPER ([8](https://github.com/Anexen/pyxirr/pull/8), [#9](https://github.com/Anexen/pyxirr/pull/9))

- NPV compatibility mode with Excel
- XIRR optimizations
- Improve the docs