add sync functions

Hey @feross 

I added `sync` **functions** like:

```
var lines = hostile.get(false)
var r1 = hostile.set('127.0.0.1', 'peercdn.com')
var r2 = hostile.remove('127.0.0.1', 'peercnd.com')
```

plus, applied these function in cmd.js
The reason that i created these functions is to simplify my codebase that used your module, 
that used for testing, mocking third-party services, so sync functions maybe more pretty simplicity.