Rounder

The v0.7.1 release comes with a new structure of the project. Now, `rounder` uses the `build-based backend which uses a `pyproject.toml` file instead of `setup.py`. The structure also integrates `doctest` with `pytest`, so now `pytest` runs all the `pytest` and `doctest` tests, also from documentation files.

This release comes with the generalization of `map_object()` to use `numbers.Numbers` instead of `Union[int, float]`. The corresponding tests have been added.

This release removes the custom exceptions from `rounder`, and instead uses the built-in `TypeError` exception, certainly customized to a particular error. This makes things easier at the user's side, as the user does not have to import these custom exception when wishing to catch the error from `rounder`.

This release comes with type annotations of the functions that create `rounder`'s API. In addition, the release fixed a bug with `signif_object()` which in particular situations changed `int` numbers to `float` ones.

This release adds generator, `map` and `filter` objects, which are now handled by the `rounder` functions - whatever a rounded `map` yields, for instance, will be rounded.

This release comes with optimized code, which performs much better for large and complex objects.