Pg: Add perl2bin() and bin2perl() conversion methods

FU/Pg.pm

@@ -758,7 +758,31 @@ C<set_type()> to configure appropriate conversions for these types.
 
 =back
 
-I<TODO:> Methods to convert between the various formats.
+Utility functions:
+
+=over
+
+=item $conn->perl2bin($oid, $val)
+
+=item $conn->bin2perl($oid, $bin)
+
+Convert the value for a specific type between the Perl representation and the
+PostgreSQL binary format, using the current type configuration of the
+connection. This is the same conversion used internally by this module to send
+bind parameters and receive query results, and map to the C<send> and C<recv>
+functions of C<< $conn->set_type() >>.
+
+These methods throw an error if C<$oid> is not a known type or if the given
+data is not valid for the type. However, these methods should not be used for
+strict validation: the conversion routines are usually written under the
+assumption that the data has been received directly from Postgres or is about
+to be sent to (and further validated by) Postgres.  For some types,
+C<perl2bin()> may return invalid data on invalid input and C<bin2perl()> may
+accept invalid binary data.
+
+=back
+
+I<TODO:> Methods to convert between bin and text formats.
 
 I<TODO:> Methods to query type info.