Expose BaseMetaDataColumn & TypeInfo

[etylermoss]

Currently when performing tasks that require knowing the full description of a SQL column, user code must re-implement types such as MetaDataColumn, TypeInfo, etc., and retrieve this data from the database manually.

Such functionality is already built into tiberius via TokenStream, see here in bulk_insert:

tiberius/src/client.rs

Line 314 in 59db579

let token_stream = TokenStream::new(&mut self.connection).try_unfold();

Could this data either be exposed by BulkLoadRequest, a new method on Client such as column_metadata(&'a mut self, table: &'a str), or at least expose the necessary types, so that user code can easily fetch & construct the metadata?