B4 documentation + testgen ~86% + B18 helper function

[sww0000]

No description provided.

[Lamarr3314]

Quality of life suggestion for integrating B4 into B18: would you be able to create a generator function which takes a precision and rounding mode and yields all of the inputs to your multiplication a and b in hex format. Here's an example of this in B5:
def getMultiplyTests(precision: str, rounding_mode:str) -> Iterator[tuple[str, str]]: yield from tests_multiply_1_2(precision, rounding_mode) yield from tests_multiply_3_4(precision, rounding_mode) yield from tests_multiply_5_6(precision, rounding_mode) yield from tests_multiply_7_8(precision, rounding_mode)