improve progress bar, add 'light' type

[epwalsh]

Adds a method CacheBuilder::progress_bar to set the progress bar type, or to disable the progess bar entirely. The options are ProgressBar::Light and ProgressBar::Full. The default when using cached-path as a library is ProgressBar::Light, while the default from the command-line is ProgressBar::Full.

The full progress bar looks like this:

while the light progress bar looks like this (and only updates every 5 seconds):

@guillaume-be let me know what you think.

[guillaume-be]

@epwalsh Thank you for working on this! I am mostly interested in the light progress bar so I will focus my comments on this.

• I am not sure how indicatif flushes the output. Because the light option indicates a time ahead of the line, my guess is that it still refreshes the output and would increment a line for every progress bar step (most likely causing a lot of logging output).

In pure Rust, I believe the below idea would actually be a very lightweight solution that would keep printing without a line return at every step (would be interesting to do a test):

use std::io::{self, Write};
use std::{thread, time};

fn main() {
    eprint!("Downloading [http://xx.ot] to [~/y/y] [178MiB] .");
    let _ = io::stderr().flush();
    for _ in 0..10 {
        eprint!(".");
        thread::sleep(time::Duration::from_millis(250));
        let _ = io::stderr().flush();
    }
    eprint!(" ✓ Done!\n");
    let _ = io::stderr().flush();

    eprint!("Downloading [http://ww.ot] to [~/z/z] [256MiB] .");
    let _ = io::stderr().flush();
    for _ in 0..10 {
        eprint!(".");
        thread::sleep(time::Duration::from_millis(250));
        let _ = io::stderr().flush();
    }
    eprint!(" ✓ Done!\n");
    let _ = io::stderr().flush();
}

[epwalsh]

@guillaume-be okay just made some updates.

[guillaume-be]

Looks great!

[epwalsh]

Great, I'll do another release once I merge this so we can push it upstream 👍