This method can be used to setup a decode/encode scheme or
perform UUID insertion. This method is especially useful for handling
MySQL spatial columns, because they need to be processed first using
the asText/GeomFromText functions.
Example:
R::bindFunc( 'read', 'location.point', 'asText' );
R::bindFunc( 'write', 'location.point', 'GeomFromText' );
Passing NULL as the function will reset (clear) the function
for this column/mode.