nullable types refactored, BaseTypeN extracted, now nullable types only need to provide dict of subtype instances
nullable datetime inherited from BaseTypeN
type system refactoring - BasePrimitiveType extracted
declaration parsing interface introducted, implemented for primitive types
output interface refactoring, type support preparation
added tests for procedure output null and default values
typo in nullable bit fixed
make_param refactoring - type autodetection code extracted as _autodetect_column_type function
output params_type finally works, for now implemented only for some of the types
missing from_declaration implemented
output can accept python types now
output refactoring, type_map removed, same column type autodetection code is used instead
output params order chagned, it's more natural to have value as a first argument
output - python types detection test added