message: Switched HashMap to BTreeMap
  Realised I move things over to a BTreeMap in lib.rs for printing results out in a nice ordering. Moved the BTreeMap into TraceMap to remove the need for that code.
diff: -use std::collections::HashMap;
  +use std::collections::BTreeMap;
  use std::path::{PathBuf, Path};
  use config::Config;
  @@ -11,7 +11,7 @@ pub struct Trace {
  pub struct TraceMap<'a> {
  - traces: HashMap<PathBuf, Vec<Trace>>,
  + traces: BTreeMap<PathBuf, Vec<Trace>>,
  config: &'a Config
  }
  @@ -20,7 +20,7 @@ impl<'a> TraceMap<'a> {
  pub fn new(config: &'a Config) -> TraceMap<'a> {
  TraceMap {
  config: config,
  - traces: HashMap::new(),
  + traces: BTreeMap::new(),
  }
  }
  