v0.7.4

#73 from migeorge/fix_testing_instructions - fixes testing instructions
#72 from migeorge/add_to_h_and_to_json - Adds to_h and to_json support to the models. Addresses issue #50. Thanks migeorge
#68 from faustinoaq/patch-1
#66 from amberframework/dj/update-docs

contributions from @migeorge to add to_json support