Implement destroy command

I have implemented rails-like `destroy` command that removes code generated by `generate` command.
@jgwhite  Looks like I only need `dasherizedModuleName`, I will just use that, is that OK?

And also we can only send `dasherizedModuleName` instead of `locals` to this function:
```javascript
Blueprint.prototype.mapFile = function(file, locals) {
  file = Blueprint.renamedFiles[file] || file;
  return file.replace('__name__', locals.dasherizedModuleName);
};
```javascript