Improve error reporting

[jrgerber]

The original dmidecode has error reporting that looks like this:

# dmidecode 3.2
Scanning /dev/mem for entry point.
# No SMBIOS nor DMI entry point found, sorry.

Things of note:

1. The version is output for all commands, not just in the help
2. The use of the "#" symbol. What is the logic for when "#" is used?
3. The failure explanation is nice and verbose

Also investigate and understand what information goes to stdout versus stderr.

[jrgerber]

Here are some original dmidecode errors:

root@UbuntuRust:~/dmidecode-rs/target/debug# dmidecode --no-sysfs --dev-mem /dev/memx -u|more
/dev/memx: No such file or directory
# dmidecode 3.1
Scanning /dev/memx for entry point.
root@UbuntuRust:~/dmidecode-rs/target/debug# dmidecode --no-sysfs --dev-mem ./dmidecode|more
# dmidecode 3.1
Scanning ./dmidecode for entry point.
# No SMBIOS nor DMI entry point found, sorry.
root@UbuntuRust:~/dmidecode-rs/target/debug# dmidecode --no-sysfs --dev-mem /sys/firmware/dmi/tables/DMI|more
mmap: Can't map beyond end of file /sys/firmware/dmi/tables/DMI
# dmidecode 3.1
Scanning /sys/firmware/dmi/tables/DMI for entry point.

The corresponding errors with Rust dmidecode:

root@UbuntuRust:~/dmidecode-rs/target/debug# ./dmidecode --no-sysfs --dev-mem /dev/memx -u|more
# dmidecode-rs 0.1.0
Error: Os { code: 2, kind: NotFound, message: "No such file or directory" }
root@UbuntuRust:~/dmidecode-rs/target/debug# ./dmidecode --no-sysfs --dev-mem ./dmidecode|more
# dmidecode-rs 0.1.0
Error: Custom { kind: UnexpectedEof, error: "Not found" }
root@UbuntuRust:~/dmidecode-rs/target/debug# ./dmidecode --no-sysfs --dev-mem /sys/firmware/dmi/tables/DMI|more
Error: # dmidecode-rs 0.1.0
Custom { kind: UnexpectedEof, error: "failed to fill whole buffer" }

The original dmidecode error messages are much more descriptive of what went wrong.

[jrgerber]

See https://github.com/mirror/dmidecode/blob/master/dmiopt.c for mutually exclusive error messages.