Use unbuffered I/O for faster printing to stdout, switch to Rustls

[sondr3]

• Use unbuffered IO for faster printing, see https://llogiq.github.io/2017/06/01/perf-pitfalls.html for more
• Use statically linked rustls over dynamically linked openssl.

Compared to the benchmark in #129 from the first post (ran hyperfine --prepare 'sync; echo 3 | sudo tee /proc/sys/vm/drop_caches' './target/release/tldr tar'). I don't know the exact command that the author of outfieldr ran, but you can also see a comparison I posted there.

Benchmark #1: ./target/release/tldr tar
  Time (mean ± σ):      29.3 ms ±   6.2 ms    [User: 1.7 ms, System: 4.3 ms]
  Range (min … max):    24.3 ms …  50.1 ms    22 runs

[niklasmohrin]

Love it, great idea

Here is what I measured on my machine

[sondr3]

Updated according to the reviews, I'm on a different computer so can't run the benchmark again but there shouldn't be a difference.

[niklasmohrin]

Having so many unwrap calls looks a bit wrong, but it is equivalent to what we had before, so... :)

[sondr3]

I actually started converting the unwraps to proper errors, but figured it was out of the scope of this PR. Happy to fix though, it may take a few days as we are celebrating our Independence Day tomorrow 😄

[sondr3]

I think I managed to fix the requested changes, this is ready for another round of reviews.

[niklasmohrin]

Great! Only thing I can really point out is that you wrote the helpful error message for writing to stdout, but discard it at the caller. I think it's better to propagate this information to the user (in the unlikely case that this goes wrong)

Other than that, thank you for your contribution 👍

[sondr3]

Done 😃

[dbrgn]

Thanks for the first round of reviews, @niklasmohrin. I'll try to take a look this weekend!

[dbrgn]

Very nice, thanks @sondr3!

The switch to RusTLS causes an increase in size of roughly 1.8 MiB (pre-strip). After stripping, the size increase is 868 KiB, which I think is fine given that OpenSSL is gone (which makes cross-compilation and static builds so much simpler).

Regarding the performance, I did a hyperfine comparison. Plain tldr which just prints the help page:

Before
  Time (mean ± σ):      12.1 ms ±   0.8 ms    [User: 1.6 ms, System: 2.7 ms]
  Range (min … max):    10.4 ms …  14.1 ms    45 runs
After
  Time (mean ± σ):      11.0 ms ±   0.7 ms    [User: 1.7 ms, System: 2.0 ms]
  Range (min … max):    10.1 ms …  13.2 ms    33 runs

And with tldr tar:

Before
  Time (mean ± σ):      14.0 ms ±   1.1 ms    [User: 1.5 ms, System: 3.2 ms]
  Range (min … max):    12.2 ms …  17.3 ms    32 runs
After
  Time (mean ± σ):      13.8 ms ±   0.8 ms    [User: 1.5 ms, System: 2.6 ms]
  Range (min … max):    12.5 ms …  15.5 ms    39 runs

Looks like a small but clear improvement. Depending on the printed page and I/O speed, it might make a bigger difference.

[dbrgn]

Thank you @sondr3!