stats: added collection of runtime statistics with handystats.

List of added metrics:
- counters:
  - 'thevoid.connections'
  - 'thevoid.active_connections'
  - 'thevoid.requests'
  - 'thevoid.requests.<code group>'
  - 'thevoid.requests.<method>'
  - 'thevoid.requests.<method>.<code group>'

- timers:
  - 'thevoid.requests.time'
  - 'thevoid.requests.<code group>.time'
  - 'thevoid.requests.<method>.time'
  - 'thevoid.requests.<method>.<code group>.time'

Here
- <code group> is response's status code group (1xx, 2xx, 3xx, 4xx, 5xx)
- <method> is request's method (e.g., GET, POST)
Version bump 0.7.0.12