v0.3.5

Refactored and added 2 methods with 2 WHERE conditions.

• is_null(field) now you can use the method for IS NULL condition
• is_not_null(field) now you can use the method for IS NOT NULL condition
• added not_null(field) method as a synonym of is_not_null(field)
• you can use those conditions with where() and having() also, usage where([['phone', "IS NULL"]]) and where([['phone', "IS NOT NULL"]])
• you can use like() and not_like() methods with no brackets []
• added _print_errors property and the same parameter for __init__() (read README for details)
• added result_dict parameter for __init__() (read README for details)
• change ? to the corresponding values in get_sql() method