Add WP-CLI command for updating minifier libraries

[westonruter]

I had been using something like this:

#!/usr/bin/env php
<?php

chdir( __DIR__ . '/../minify' );

$sources = array(
    "JS/ClosureCompiler.php" => "https://raw.github.com/mrclay/minify/master/min/lib/Minify/JS/ClosureCompiler.php",
    "JS/JSMin.php" => "https://raw.github.com/mrclay/minify/master/min/lib/JSMin.php",
    "JS/JSMinPlus.php" => "https://raw.github.com/mrclay/minify/master/min/lib/JSMinPlus.php",
    "CSS/Compressor.php" => "https://raw.github.com/mrclay/minify/master/min/lib/Minify/CSS/Compressor.php",
    "CSS/UriRewriter.php" => "https://raw.github.com/mrclay/minify/master/min/lib/Minify/CSS/UriRewriter.php",
    "CommentPreserver.php" => "https://raw.github.com/mrclay/minify/master/min/lib/Minify/CommentPreserver.php",
);

foreach( $sources as $path => $url ) {
    echo "$path => $url\n";
    $contents = file_get_contents( $url );
    file_put_contents( $path, $contents ) || exit(1);
    system( sprintf( 'git add %s', escapeshellarg( $path ) ) );
}