GRIB2: added support for snow level (level type 114)

ChangeLog

NEWS

doc/tex/c_ref.tex

doc/tex/c_vlist_att.tex

doc/tex/c_vlist_var.tex

doc/tex/c_zaxis.tex

doc/tex/cdi_cman.tex

doc/tex/cdi_fman.tex

doc/tex/f_ref.tex

doc/tex/f_vlist_att.tex

doc/tex/f_vlist_var.tex

doc/tex/f_zaxis.tex

doc/tex/formats.tex

doc/tex/zaxis.tex

src/cdi.h

src/gribapi.h

src/stream_grb.c

src/stream_gribapi.c

src/zaxis.c