Introduce pFq1m for evaluation near z = 1?

This would be like how `log1p(z)` is more relatively accurate for small argument than `log(1+z)`. The use of `1m` makes sense here with respect to the branch cut.

Then, evaluating an elliptic integral near unity, such as `K(1-1/α^2)` for large `α` could be converted to a call to some `K1m(1/α^2)` that calls the appropriate `_₂F₁1m`.