add config file to read

[fuchao2012]

add a config file , used for repacking again

just like:

epi --file="epi.json"

epi.json

{
 ...
  version: '1.4.0',                                                                           
  out: '/path-to-project/angular2-electron/releases',                   
  'app-bundle-id': '',                                                                        
  'app-version': '',                                                                          
  overwrite: true,                                                                            
  asar: false,                                                                                
  icon: 'assets/icon.icns',                                                                   
  app_version: '0.0.1',                                                                       
  bundle_id: '',                                                                              
  appname: 'image-size-calculator',                                                           
  sourcedir: 'build',                                                                         
  ignore: '/path-to-project/angular2-electron/releases' } 

[vrunoa]

@fuchao2012 great idea. Care to drop a PR ? Otherwise i'll try to implement this myself. It may take some time.