standardlastprofile 2.0.1

• The BDEW gas Leitfaden reference URL was updated: the previous link returned
  a 404. References now point to the current edition (KoV XV, 2026-03-27) via a
  stable Internet Archive permalink. The SigLinDe coefficients and method are
  unchanged from the previous edition.

• slp_gas(), slp_gas_kundenwert(), and slp_gas_coefficients() now also
  accept a numeric 34 / 33 for the variant argument, in addition to the
  character forms "34" / "33".

• Added input validation: slp_gas_siglinde() now checks that each of its nine
  coefficients is a single finite numeric, and slp_gas() /
  slp_gas_kundenwert() reject temperatures >= 40 (the SigLinDe pole) with an
  informative error.