Add column comments and bugfixes

0.10.23

✨ Features

• Add ability to pass comment to sqlalchemy when creating a column #485

🐛 Fixes

• Fix LargeBinary fields that can be nullable #409
• Make ormar.Model pickable #413
• Make first() and get() without arguments respect ordering of main model set by user, fallback to primary key (asc, and desc respectively) #453
• Fix improper quoting of non-aliased join on clauses in postgress #455