! statsd,datadog: reformat metric names to get a better display of automatically named traces, closes #35

After a bit of testing it seems like instead of  generating more friendly names by default, we need to do
changes that are specific to each module (StatsD and Datadog) in order to make it work properly. Here is
a list of the introduced changes:
  - StatsD
    - Change dots (.) to underscores (_) on the host name string.
    - Change ': ' to single underscore and spaced to underscore. Userful for automatically generated http
      trace names.
    - Change '/' to underscore. Ideally the dashboard could replace '_' with '/' to display it like a path.

  - Datadog
    - Change ': ' to ':'. Userful for automatically generated http trace names.