Add option to read from stdin #29
Description
Support for writing to stdout was requested in #25 so guardonce could be integrated with other tools. I considered adding support for reading from stdin to go along with that, but eventually decided against it due to time constraints. It's still a good idea, though, so it's going in the backlog.
One trick to this is that reading from stdin implies writing to stdout, because where else would we put the output? I was thinking I'd name the flag --stdio to make that fact really obvious, but --stdin seems to be the less surprising name. So, I'll probably just name the flag --stdin.
Another consideration is the path. The input file path is often used for generating the include guard pattern, but guardonce doesn't know the actual file path if input comes from stdin. There needs to be a way to explicitly pass guardonce that information, so we'll add an --assume-filepath=<file> option to do so.
--assume-filepath will be required when using --stdin together with --pattern for guard2once or checkguard and will be required even when using --stdin alone for once2guard. The difference here is because once2guard always uses a pattern—if you don't specify one, it just uses a default pattern.