LogEvent(string, map) and requested unit test

@dkorolev PTAL
Why not use a single flag instead of two: ```--value``` and ```--pairs```?

And an example command line in the very top of this file would help.

Plus: 1) ```---event``` could default to some ```"test"```, to simplify the command line, and 2) ```--url``` is best to rename into some ```--alohastats_url``` and default to some ```http://localhost:808```.