f3* should use exit codes

[abma]

currently they always exit with "0":

when read errors / writte errors happen, it should use a non-zero exit code!

https://github.com/AltraMayor/f3/blob/master/f3read.c#L442
https://github.com/AltraMayor/f3/blob/master/f3brew.c#L477

[AltraMayor]

F3 returns an error when it cannot report on the tested drive. That is, F3 does not try to interpret the output of its report.

Although I'm suspicious of the value that these interpretations can actually add, I'm open to a pull request to add a command-line parameter to return such an error code.

[abma]

F3 returns an error when it cannot report on the tested drive. That is, F3 does not try to interpret the output of its report.
Although I'm suspicious of the value that these interpretations can actually add, I'm open to a pull request to add a command-line parameter to return such an error code.

This allows it to be run inside a script. ATM the output has to be parsed which is error-prone. Basicly all (unix) command line tools heavily use exit codes.

In other words: i don't care about the output, i only want to know if the data was correctly written and if it was correctly read.