message: feat(debug): Report asset files
  `cobalt debug files assets` will report all files found to be assets.
  This allows for quick sanity checking when debugging cobalt's processing
  and produces less noise if wanting to use `--trace` to see why the
  ignore patterns are doing what they do.
diff: use clap;
  use cobalt;
  +use args;
  use error::*;
  pub fn debug_command_args() -> clap::App<'static, 'static> {
  @@ -10,6 +11,12 @@ pub fn debug_command_args() -> clap::App<'static, 'static> {
  .about("Print syntax-highlight information")
  .subcommand(clap::SubCommand::with_name("themes"))
  .subcommand(clap::SubCommand::with_name("syntaxes")))
  + .subcommand(clap::SubCommand::with_name("files")
  + .about("Print files associated with a collection")
  + .args(&args::get_config_args())
  + .arg(clap::Arg::with_name("COLLECTION")
  + .help("Collection name")
  + .index(1)))
  }
  pub fn debug_command(matches: &clap::ArgMatches) -> Result<()> {
  @@ -29,6 +36,24 @@ pub fn debug_command(matches: &clap::ArgMatches) -> Result<()> {
  _ => bail!(matches.usage()),
  }
  }
  + ("files", Some(matches)) => {
  + let config = args::get_config(matches)?;
  + let config = config.build()?;
  + let collection = matches.value_of("COLLECTION");
  + match collection {
  + Some("assets") => {
  + for file_path in config.assets.files() {
  + println!("{:?}", file_path);
  + }
  + }
  + None => {
  + bail!("Must specify collection");
  + }
  + _ => {
  + bail!("Collection is not yet supported");
  + }
  + }
  + }
  _ => bail!(matches.usage()),
  }
  