Moved exception handling functions in goes.py to new module, exceptions.py.
In goes.py, added import exceptions.
Moved all csv files and scripts to create them to new directory,
instr_files.  Created global variable in goes.py, INSTR_FILES_PATH,
 pointing to this new location and added it to places where csv
files are called.
Tidied docstrings a little in exceptions.py
Changed default values of varname keywords of functions in exceptions.py