add support for parser keywords specifying to multiple deck keywords

Say hello to the complete set of well, region, field and group output
specifiers soon...
avoid illegal internal names in the MULT keywords

before this, the variants with the trailing minus were just silently
ignored, and even if they were not, the code generator would have
produced illegal code, because the keyword name is used for a C++
variable there, i.e. the names needed to be valid names in the C++
sense. "Happily", these the former bug canceled the latter, so the
build went through...

now, there is only one internal keyword called "MULT_XYZ" which
matches on all possible variants which are allowed in a deck. The
mechanism used is a deck name list...
use deck keyword name list for the well output specifier keywords