Statsite

- Multiple "-c" configuration files can be passed to `statsite`.
- If a configuration file doesn't exist or contains a parse
error, and error will be raised.
- Try to increase socket buffer size for UDP to avoid packet
loss when the buffer is full during high load.
- Prefix key-value entries with "kv"

- Class to load for various components can be passed to the
configuration as a string.

- Add a TCP "aliveness_check" option for easier monitoring.
- Fix off-by-one issue in calculating percentile statistics.

- Initial release