Version 2.0 Rollout

[ablodge]

To do items for the rollout of amr-utils v2.0:

• Testing and Documentation of amrs.py
• Testing and Documentation of amr_readers.py
• Testing and Documentation of amr_writers.py
• Testing and Documentation of amr_iterators.py
• Testing and Documentation of amr_graph.py
• Testing and Documentation of amr_alignments.py
• Testing and Documentation of amr_normalizers.py
• Testing and Documentation of smatch_utils.py
• Testing and Documentation of propbank_utils.py
• Testing and Documentation of amr_visualizers