false positive SIG305 after common abbreviations

[jshwi]

The sentence tokenizer treats a period as a sentence boundary unless the
preceding token is in a small set of known abbreviations. That set only holds
e.g., i.e., mr., dr., vs., etc. and u.s., so other common
abbreviations end a sentence and the lowercase word after them is reported as
SIG305 (description not capitalized).

Reproducer:

def function(a: int, b: int, c: int) -> None:
    """Summary.

    :param a: The threshold, cf. the parent class.
    :param b: No. of items to keep.
    :param c: The layout in fig. 3, per Smith et al. and others.
    """

$ docsig .

Each parameter description is flagged with SIG305 even though cf., no.,
fig. and et al. are abbreviations, not sentence endings.