• refactored schema builder

• support drop index

• support drop foreign key

• support drop private key

• clear cache after modification schema

fixed cache issue

• fixed cache issue. Cached queries work now

• save/load dynamic structure
• load current database schema
• support Composite Primary key in cache queries
• the ability drop tables, views, columns and sequences
• examples of CTE with and without cache
• examples of Union/Union with and without cache
• fixed some bugs