#358 rexxref DATE docs wrong for D as input format

[Josep Maria Blasco]

Location: rexxref 5.2.0, §7.4.24 (DATE), p. 452, says: The option2 format must specify day, month, and year (that is, not "D", "L", "M", or "W").

This incorrectly excludes 'D' (Days) from the valid input formats. The interpreter happily accepts "D" as an input format. For example:

DATE("N", "100", "D") --> "10 Apr 2026"

Furthermore, when an invalid input format is supplied (e.g., DATE("N", "foo", "X")), the interpreter's error message (Error 40.904) lists the valid input options as BDEFINOSTU, which explicitly includes D.