Add an option to force writing to stdout

[gavinhoward]

This comes from this HN thread.

Since rep always opens a pager (except for one page?), it interferes with the editor opening at the same time.

So I added --stdout to force rep to output to stdout.

This PR may not be great. I am not a Rust programmer, and I admit that I did it in the dumbest way possible.

I'm open to harsh criticism here since this is my first public contribution using Rust. This includes criticism about how I implemented this.

I also tried running rustfmt, but it screamed about being deprecated. I tried installing rustfmt-nightly, and it failed. So if style is wrong, I'm sorry, and I'll fix it manually.

[gavinhoward]

Oh, and I understand if this is not something you want. :)

[robenkleene]

Thanks @gavinhoward we definitely want to support the use case from the Hacker News comment! I added a couple of minor comments to PR, address those and we'll merge this.