PyPi release 1.7.4

What's Changed

• Association vocab keying tweaks by @karlcz in #180
• datapath fix for missing delete method on table wrapper by @robes in #179
• adds cascading drop to ermrest model and unit tests by @robes in #181
• Generalize reference targets for Table define utility methods by @karlcz in #183
• add custom repr to ermrest model classes by @karlcz in #184
• Initial "model management operations" package by @robes in #185
• MMO x DDL by @robes in #186
• add Table.sqlite3_ddl() method that returns a SQL DDL statement by @karlcz in #187
• Various bugfixes (11bbafe, 5b3c585, b24930c, 19e4eac) by @mikedarcy

Full Changelog: v1.7.3...v1.7.4