implement extension file type with a list
extension : improve code
implement clear_elements() to clear a char * chained list
remove use of file_type now we have a proper file extension list
implement specific files with a chained list
implement parse_args()
improve usage() and manpage
implement -I to ignore some files
bug #28
fix clear_elements()
update manpage and usage() for I option
bug #28
improve manpage