CheckColumn constraint, ReferentialAction and bug fixes

0.11.3

✨ Features

• Document onupdate and ondelete referential actions in ForeignKey and provide ReferentialAction enum to specify the behavior of the relationship (by @SepehrBazyar - thanks!) #724
• Add CheckColumn to supported constraints in models Meta (by @SepehrBazyar - thanks!) #729

🐛 Fixes

• Fix limiting query result to 0 should return empty list (by @SepehrBazyar - thanks!) #766

💬 Other

• Add dark mode to docs (by @SepehrBazyar - thanks!) #717
• Update aiomysql dependency #778