Print with newline edge cases

[killercup]

I ran clippy on diesel-rs/diesel#1428 and it gave the following warnings:

error: using `print!()` with a format string that ends in a newline, consider using `println!()` instead
  --> src/comment.rs:28:9
   |
28 |         print!("===============\n\n");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> src/main.rs:1:9
   |
1  | #![deny(warnings)]
   |         ^^^^^^^^
   = note: #[deny(print_with_newline)] implied by #[deny(warnings)]
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.177/index.html#print_with_newline

error: using `print!()` with a format string that ends in a newline, consider using `println!()` instead
  --> src/post.rs:56:5
   |
56 |     print!("\n");
   |     ^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.177/index.html#print_with_newline

These are not wrong but also not helpful: We want to explicitly write a number of new lines.

[sgrif]

Hilariously, I only wrote print!("\n") over println!("") because I could have sworn clippy complained on empty string to println!

[killercup]

I could have sworn clippy complained on empty string to println!

It wants you to use println!();. Let me open an issue to add a suggestion for that: #2319.

[basil-cow]

duplicate of #2990, can now be closed @flip1995