make lodash a dependency

I tried to checkout dat, and ran npm test, but get 

```
Error: Cannot find module 'lodash'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (/Volumes/untitled/github/random/dat/node_modules/sleep-ref/memstore.js:1:71)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:364:17)
```

Looking at memstore.js it looks like more features of lodash are being used. Just include all of lodash for now.
Merge pull request #15 from ryanramage/patch-1

make lodash a dependency