Use of labels causes crash

[mattcarabine]

The following input program will cause Kami to crash:

foo:
   for (i=0; i<10; i++){
    if (i===4){
      break foo;
    }
  }

Output:

$ ./bin/unused test.js
TypeError: handlers[node.type] is not a function
    at exec (/Users/matt/Downloads/node-unused/index.js:35:28)
    at /Users/matt/Downloads/node-unused/index.js:245:9
    at Array.forEach (<anonymous>)
    at unused (/Users/matt/Downloads/node-unused/index.js:244:10)
    at /Users/matt/Downloads/node-unused/bin/unused:38:27
    at Array.forEach (<anonymous>)
    at Object.<anonymous> (/Users/matt/Downloads/node-unused/bin/unused:35:8)
    at Module._compile (internal/modules/cjs/loader.js:721:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:732:10)
    at Module.load (internal/modules/cjs/loader.js:620:32)

This is because LabeledStatements are not handled, see the parsed output from Prisma on http://esprima.org/demo/parse.html for this program.

The fix is to instead handle LabeledStatements within index.js.

[tannerkc]

@mattcarabine https://www.npmjs.com/package/reveal-unused?activeTab=readme