version 2.4 released

The period g0 for the SYNOP group 54g0sndT (section 3) defaults to the W1W2 period; timeBeforeObs is used instead of hoursFrom, hoursTill (not backwards compatible). Various additional METAR, SYNOP and BUFR groups are recognised, changes for FMH-1 (2017) were incorporated, and a few bugs were fixed.