The "only-printable" mode will only generate printable inputs for the fuzzed program. This might be useful for many applications such as expr(1). The changes to achieve this are:

1. Add an option and configuration flag for the "only-printable" mode;
2. Change the initial single-byte input from '\0' to ' ' (a space character) under this mode;
3. Implement the printable version of mangle functions;
4. Add initialization function to reset the mangle function list.

The printable version of "mangle_Magic" is currently implemented as directly transferring the original data to printable outputs. Because I don't know the semantics of this function. If anyone has any suggestion for this, I'd like to improve it.