Improve test coverage, extract function for better testing

Improve test coverage, extract function for better testing

Add files to test EU::PXS::Utilities::map_type(), valid_proto_string(),
process_typemaps().  Extract code for processing a single typemap file
into its own sub, thereby permitting more focused testing.  Eliminate some
unreachable branches and conditions in process_typemaps().

On the basis of coverage analysis, eliminate unreachable code.
Reformat some code for readability (shorter line length).