Add CLI script to format files

[bartveneman]

• Write to stdout, do not overwrite files
• Add readme section for CLI
• Add help section to CLI and show that in readme as well
• use Node's parseArgs to setup argument handling and typing
• Do not add extra dependencies

format-css styles.css
format-css styles.css --minify
format-css styles.css --tab-size=2

cat styles.css | format-css
cat styles.css | format-css --minify
cat styles.css | format-css --tabs-size=2