Some nice features

I've been using a modified version of audiosprite, but now I decided to share those modifications, which include:

- Options to specify path for the files URL's on the generated JSON
- Basic Howler.js JSON format
- Silence gap duration selection
- Option for specifying minimum sound duration (had some bugs on iOS when using sounds with less than 50 milliseconds)
- Some extra file types

What do you guys think?