A set of changes intended to make the hydrogen and helium versions of
the code more similar.
Note that the temperature and ionization fraction arrays now are
structures.
Fixed some errors in the way the temperature structure was programmed.
Merge branch 'master' of github.com:garrelt/C2-Ray3Dm

Some local editing of mat_ini_cubep3m.F90 (introducing temperature
structure) and remote editing (on sfinx).
Wrapped the declaration of tn (thread number) variable into preprocessor
statements for OpenMP.
Changed the unit number for the time file. It was 31 but this could be
the unit number of a log file for MPI process 1.
Added definition of hydrogen abundance (by number). For consistency
with the helium version.