small bugfix in hex2bin()
separate stdout and stderr to allow piping
improve decryption performance

"blowfish-compat" is used, making reverseWords() unnecessary.
The decryption was corrected (see source comment).
The buffer size is more convenient now.
add proper password prompt, cURL error handling

also fixed some small memory leaks
check input and output file integrity

Makefile: -O3 in CFLAGS makes MD5 calculation significantly faster
add cache file for passphrases
use fwrite() instead of write()

If there is no space left on the output file system, write() returns
a short item count, but errno is not set. So otrtool will exit, but
report "error: Success".