Use Redis if available else default to LevelDB

[nelsonic]

As the title suggests, we check for the presence of Redis and use it if available:

// pseudocode
if(redisAvailable) {
  var db = require('redis');
} else {
  var db = require('level');
}

[nelsonic]

This is an implementation detail ... feels like it should be left to the user/implementor to decide.
What do people think? should we add this type of DB-switching code to our demo?

[joseluisq]

Sure, I like the checking idea if Redis is available. 👍

Well, here some "interesting" benchmarks 😄
http://vschart.com/compare/leveldb/vs/redis-database