Add the -i, -o flags, and other improvements

[The-King-of-Toasters]

• Only check for invalid flag combinations once, outside the switch.
• Pass os.Files for each function instead of using stdin/stderr by default.

The last comment replaces the use of fmt.Printf with file.WriteString. This may fix #2, but I don't have a Windows system on hand to check.

[FiloSottile]

Hey, thanks for contributing, but as I mentioned in the README and in #3 (comment), I am actively developing this and already conflicted over these changes :(

Can you help me understand why would replacing fmt.Printf help? I could see Println adding CRLF, but I'd be surprised by Printf doing that.

[The-King-of-Toasters]

Hey, thanks for contributing, but as I mentioned in the README and in #3 (comment), I am actively developing this and already conflicted over these changes :(

That's fine. I thought by adding a couple small changes that they would get through. I'm happy to step aside on this :).

Can you help me understand why would replacing fmt.Printf help? I could see Println adding CRLF, but I'd be surprised by Printf doing that.

I though that writing direct to a file would solve #2, but that seems to be a auto-conversion issue with PowerShell. It was also a way to get rid of fmt, as it was only used for those three lines.

Other than the Printf issue, is there any other change that's conflicting?

[The-King-of-Toasters]

Actually, I can see a lot wrong with my work so far. Closing.