Lack of signal handling

[13k]

• Ruby version: Not applicable
• Rubyfmt git sha: 5ebcd9f

Input file

Any input, immediately followed by any signal (tested SIGINT or SIGTERM).

Or reading from tty's stdin, typing anything, Ctrl-C, then Ctrl-D.

Rubyfmt's output

Not applicable.

This breaks because

Reading from tty, segfaults (on Linux):

> target/release/rubyfmt-main 
hello world
^CSegmentation fault (core dumped)

Sending a signal to the process, main thread panics:

> { target/release/rubyfmt-main < librubyfmt/ruby_checkout/ruby-2.6.6/lib/irb.rb & }; pkill -INT rubyfmt-main
[1] 1307711
thread 'main' panicked at 'bad init status: Interrupt', src/main.rs:119:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
[1]+  Exit 101                target/release/rubyfmt-main < librubyfmt/ruby_checkout/ruby-2.6.6/lib/irb.rb

I'm not sure about what to do when handling signals during processing with non-interactive inputs (process stdin or files), specially if it's running in "in place mode" (probably write results when it's guaranteed formatting is finished); but when reading from tty, I'd expect to be able to cancel and exit the process with SIGINT, like (most) command-line tools do.