requirable version of Date.now()

 Use-case is to be able to mock out Date.now() using require interception.
 For example
 var now = require("date-now")
 var ts = now()
 var ts2 = Date.now()
 assert.equal(ts, ts2)
 Example of seed:
 var now = require("date-now/seed")(timeStampFromServer)
 // ts is in "sync" with the seed value from the server
 // useful if your users have their local time being a few minutes
 // out of your server time.
 var ts = now()
 .
 Node.js is an event-based server-side JavaScript engine.