Extract function find_gcov_files

Extracted the function "find_gcov_files" from the massive "process_datafile" function.
Extract function find_potential_wd

Extracts the function "find_potential_wd" from the (now less) massive function
"process_datafile".
Extract class Gcov

Move all functionality related to gcov execution into the class "Gcov".  The
function "process_datafile" is now starting to look decent.