Automated argument count aliases.

Argument count exception handling and testing aliases (e.g.,
die_unless_args_3_to_7()) are now automatically generated in a similar manner as
variable type exception handling and testing functions (e.g.,
die_unless_variable_float()). Needless to say, such automation results in a
dramatically more streamlined and maintainable @{*-core/*-alias/*-core/*-arg}.
Unrelatedly, :define_function_if_pathable() now has a reasonable stab at a first
working implementation. More for the morrow, as She will.