[x] modified handling of empty graphs in from_edge_list
[x] special handling of p=0 and m=0 in erdos_renyi random graphs (for efficiency)
[x] fixed bug in generative_models.molloy_reed that resulted in wrong degree sequences
[x] added unit tests for empty graphs and molloy_reed model
[x] added tutorial notebook for generative models
[x] stochastic_block_model now returns undirected graph (matching the documentation)
[x] added unit test for stochastic block model
[x] bumped version number to 0.2.0 to make it easier to identify version with updated API -> should move to 1.0.0 as soon as API restructuring, testing and documentation are complete
from_edge_listgenerative_models.molloy_reedthat resulted in wrong degree sequencesmolloy_reedmodelstochastic_block_modelnow returns undirected graph (matching the documentation)