Retry with exponential backoff

Merge pull request #33 from Joneser/master

Add retry logic to requests

Network timing

This release adds support for recording request timings:

client.request({ timing: true }).then(response => {
    console.log(response.timings);
    /* {
           socket: 10,
           lookup: 30,
           connect: 60,
           response: 100,
           end: 150
      } */
    console.log(response.timingPhases);
    /* {
           wait: 10,
           dns: 20,
           tcp: 30,
           firstByte: 40,
           download: 50,
           total: 150
      } */
})

Request timeout

Added socket timeout and dropRequestAfter options for controlling timeouts and aborting requests upon reaching those tiemeouts.

Convenience Release

This release is mostly focused on internal cleanup, but also contains change to allow to specify default params for the request when constructing the client.