0.52.0

Lots of improvements to piccolo schema generate:

• Dramatically improved performance, by executing more queries in parallel (courtesy @AliSayyah).
• If a table in the database has a foreign key to a table in another schema, this will now work (courtesy @AliSayyah).
• The column defaults are now extracted from the database (courtesy @wmshort).
• The scale and precision values for Numeric / Decimal column types are extracted from the database (courtesy @wmshort).
• The ON DELETE and ON UPDATE values for ForeignKey columns are now extracted from the database (courtesy @wmshort).

Added BigSerial column type (courtesy @aliereno).

Added GitHub issue templates (courtesy @AbhijithGanesh).