Control destpath

### Actual

``` js
var files = init.filesToCopy(properties); // { "foo.js": "project/root/foo.js" }

for (let file in files) {
let to = path.join('MY_CUSTOM_DIRECTORY', file);
let from = files[file];

delete files[file];
files[to] = from;
}

init.copyAndProcess(files, properties);
```

It's real pain to understand how it works.....
### Expected

``` js
var files = init.filesToCopy(properties, {
dest: 'MY_CUSTOM_DIRECTORY' // or something else...
});
// { "MY_CUSTOM_DIRECTORY/foo.js": "project/root/foo.js" }

init.copyAndProcess(files, properties);
```