This patch introduces a new structure holding partial pressures (doubles in bar) for
all three gases and a helper function to compute them from gasmix (which holds fractions)
and ambient pressure. Currentlty this works for OC and CCR, to be extended later to PSCR.
Currently the dive_comp_type argument is unused.
Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>