Clarify semantics of fancy integer division functions.

Closes #88 (closed).

The goal of these functions is to provide fast, fp-free functions for semi-complicated semantics on positive integers (The old implementation did not behave sensibly for negative input). This MR clarifies the names and docstrings of the fancy integer divisions to make it clear that negative input is not always expected. Furthermore, the implementation is changed such that no remainders or conditionals must be evaluated.

The old names are still available but issue deprecation warnings.