folderify transform

Added [folderify](https://github.com/parroit/folderify) to tranforms.

Folderify inline a whole directory content in browserify results.
 
1. It uses falafel to intercepts calls to [include-folder](https://github.com/parroit/include-folder) 
2. use include-folder to generate source code of a function with a fs.readFileSync call for each file in directory
3. feed brfs stream with generated source code 
4. replace include-folder call with brfs output