Add struct_builder helper and start using it
to_mx_class_id: add Int[32|64] types
make_mx_array<vector<string>> return 0 if empty
make_mx_array: overload for optionals
mx_make_array: generic templ. for arithmetic types
use struct_builder for dim_to_struct (Sampled)
remove make_mx_array overload for uint32_t