add io functions and functionpointer types module
add file io to intset
use io module
remove inline, would not apply
remove stray >
Change io from hard exit to using GtError
fix logic errors, cosmetics, assertions

lots of cosmetic changes
added assertions for set errors
fixed two cases of logical faults !had_err -> had_err
make function easyer to use and fix comment
Merge pull request #315 from Garonenur/intset

file io