Both were sliced from the year string, so years with other than four
digits gave the wrong century and two-digit year, and %y was a string
that the - and _ flags could not unpad. Compute them arithmetically and
pad them to two digits, matching Ruby's strftime.
%N renders the fractional part of the second. The milliseconds returned by
getMilliseconds() are the three most significant digits of that fraction and
must be zero-padded to three digits before use, otherwise sub-100ms values
lose their leading zeros:
50ms => strftime("%N") returned "500000000", expected "050000000"
5ms => strftime("%3N") returned "500", expected "005"
Pad the milliseconds to three digits before slicing to the requested width.
As written, the strftime module's `getSuffix` method (responsible for
returning a date's ordinal string) works correctly for all dates in a
month _except_ 11, 12, and 13.
The existing code would return a string based on the last digit of the
date. In American English, these three dates use the `th` suffix rather
than `st`, `nd`, or `rd`.
This refactor/bug fix draws inspiration from Rails' ActiveSupport
ordinal inflector:
https://github.com/rails/rails/blob/main/activesupport/lib/active_support/locale/en.rb
The Ruby code above is designed to work with any number, so the bug fix
to this library is simpler.
The test suite is also updated with additional examples to verify the
correctness of these changes.
