Add support for trimix gas changes.
Add support for trimix gas changes.

The second gas change event (type 0x06) contains both the oxygen and
helium percentages. These are now reported correctly with the new
GASCHANGE2 event.

glance-/libdivecomputer,Poltsi/libdivecomputer-vms,henrik242/libdivecomputer,venkateshshukla/libdivecomputer,josh-wambua/libdivecomputer,henrik242/libdivecomputer,venkateshshukla/libdivecomputer,josh-wambua/libdivecomputer,glance-/libdivecomputer