code: function findBinaries(env) {
  	return _.filter(_.flatten(_.map(_.filter(env.split(':'), fs.existsSync), readdir)), permissions.isExecutable);
  }
docs: /*
  finds all binaries in the user's $PATH
  
  - get a list of all dirs in the path by splitting env.PATH on ':'
  - filter out those that don't exist (fs.existsSync)
  - read all of these dirs by mapping readdir to the list
  - this gives us an array of arrays, flatten it
  - finally filter out all file in the path that aren't marked as executable