Piecewise-regression

Changes:

- Modified the Davies test for the existence of one breakpoint to use the Wald test as a test statistic, following Muggeo, V. M. (2008). Segmented: an R package to fit regression models with broken-line relationships. R news, 8(1), 20-25.
- Added tests for the Davies test with a range of data models.
- Added the option to get model fit parameters easily with a convenience function `get_params` on the Fit object.
- Added the option to get data predictions easily with a convenience function `predict` on the Fit object.
- Made small changes in response to issues raised.

What's Changed
* Create LICENSE.txt by chasmani in https://github.com/chasmani/piecewise-regression/pull/1
* Edit suggestions by galessiorob in https://github.com/chasmani/piecewise-regression/pull/2

New Contributors
* chasmani made their first contribution in https://github.com/chasmani/piecewise-regression/pull/1
* galessiorob made their first contribution in https://github.com/chasmani/piecewise-regression/pull/2

**Full Changelog**: https://github.com/chasmani/piecewise-regression/commits/v1.2.0