Numcertain

Added:
- Getter UFuncs for the nominal and uncertain components of `ndarray`s of `uncertain` values
- Builds for `musllinux`

Changed:
- Moved the `uncertain` type to `numcertain.uncertain`

Added:
- Equality & inequality for the `uncertain` python type & numpy dtype
- Tests covering all aspects of the `uncertain` python type & numpy dtype
- A `nominal` and `uncertainty` property to the `uncertain` python type

Fixed:
- Relaxed unnecessarily strict dev dependencies
- Documentation surrounding the computation of uncertainties for multiplication and division

Removed:
- Casts to & from the numpy `float16` type

Initial release of the numcertain package, supporting the following features:

- Storage and retrieval of uncertain values with the uncertain type
- Instantiation of uncertain values with pairs or single ints or floats
- Basic arithmetic with uncertain values (addition, subtraction, multiplication & division)
- Conversion to and from ints and floats
- Hashing of uncertain values
- Pretty printing of uncertain values
- Retrieval of nominal and uncertain components
- Basic arithmetic with numpy arrays of uncertain values (addition, subtraction, multiplication & division)