Make logging more human friendly

[tadatuta]

now

require('@bem/walk')(['blocks']).on('data', console.log);

results in

BemFile {
  cell:
   BemCell {
     _entity: BemEntityName { block: 'b1' },
     _layer: 'blocks',
     _tech: 'css' },
  path: 'blocks/b1/b1.css' }