Fixchksum reads an Intel hex file, computes the checksum for each record,
and if it doesn't match the checksum in the record, writes out a new file
with the proper checksum(s).

If you modify data in a hex file with a text editor, the record must remain
the same length as the original. Only the data may be changed.

The output file will only be written if one or more records have been fixed.
The file will have the same name as the input file, but with the ".hex"
extension replaced with "-fixed.hex". The original hex file is not modified.

Example:

  fixchksum test.hex

reads the file 'test.hex' and generates a file 'test-fixed.hex'.