Add support for check constraints

[lycantropos]

We should add support for check constraints (both their generating & handling in records creation).

[lycantropos]

I can see that like:

1. If constraint's sqltext field is an SQLAlchemy expression, we can convert it to plaint string based on dialect using statement compiler like

dialect.statement_compiler(dialect, None).process(constraint.sqltext, 
                                                  include_table=False,
                                                  literal_binds=True)

2. We need to parse string and obtain SQL AST (e.g. there are lark parser generator and SQL language BNF).
3. Transform SQL AST to Python AST (e.g. x BETWEEN start AND end will become start <= x <= end).
4. Build AST.Lambda with parameters corresponding to columns using compile.
5. Use built lambda in strategy.filter.