3.1.0

• Tests structure has been updated for easier DBMS switching
• Added tests for PostgreSQL and SQLite
• Added warning for unsupported SQLite migration commands
• Fixed bug with schema type map missing when loading PostgreSQL schema
• Added fallback for SQLite primary key detection
• Schema type is now passed to TableColumn and TableChange
• Changed the way column length is compared
• Column length is now present only for DBMS supporting it
• Updated Travis config for MySQL explicit_defaults_for_timestamp setting