Implement schema UDF API

[dkropachev]

APIs to cover:

cass_keyspace_meta_function_by_name
cass_keyspace_meta_function_by_name_n
cass_function_meta_body
cass_function_meta_name
cass_function_meta_full_name
cass_function_meta_body
cass_function_meta_language
cass_function_meta_called_on_null_input
cass_function_meta_argument_count
cass_function_meta_argument
cass_function_meta_argument_type_by_name
cass_function_meta_argument_type_by_name_n
cass_function_meta_return_type
cass_function_meta_field_by_name
cass_function_meta_field_by_name_n
cass_iterator_functions_from_keyspace_meta
cass_iterator_get_function_meta