GraphGallery 0.1.8

Changes:

• Add DAGNN implementation
• fix some typos
• rewrite __getattr__ in BaseModel, so most of the attributes can be used when calling model.attr instead of model.model.attr, e.g.,
  • model.summary equals model.model.summary if has this attribute
  • model.layers equals model.model.layers if has this attribute
  • model.weights equals model.model.weights if has this attribute
  • others like get_weights(), trainable_variables, variables are the same