Documentation and testing improvements

Fixed up the README to be accurate and also more test coverage.

-------------------------|-----------|-----------|-----------|-----------|
File                     |   % Stmts |% Branches |   % Funcs |   % Lines |
-------------------------|-----------|-----------|-----------|-----------|
   lib/                  |      99.1 |     95.45 |       100 |      99.1 |
      EphemeralSocket.js |      97.1 |     91.18 |       100 |      97.1 |
      backoff.js         |       100 |     83.33 |       100 |       100 |
      dns-resolver.js    |       100 |     96.67 |       100 |       100 |
      messages.js        |       100 |       100 |       100 |       100 |
      packet-queue.js    |       100 |       100 |       100 |       100 |
      statsd-client.js   |       100 |       100 |       100 |       100 |
-------------------------|-----------|-----------|-----------|-----------|
All files                |      99.1 |     95.45 |       100 |      99.1 |
-------------------------|-----------|-----------|-----------|-----------|


This also contains some fixes:

 - [cleanup]: Call .send() with one arg in lib/statsd-client.js
 - [feature]: Allow dnsResolve options in lib/statsd-client.js
 - [lint]: Fixup lib/statsd-client.js to use single quotes
 - [bugfix]: Fix off by one in the prefix code in lib/statsd-client.js
 - [bugfix]: Allow socket_timeout to be 0 in lib/Ephemeral-socket.js

cc @sh1mmer @kriskowal