than io.Readers and io.Writers.
change the Encoder/Decoder protocol so that each message is preceded by its length in bytes.
R=rsc
DELTA=468 (119 added, 23 deleted, 326 changed)
OCL=31700
CL=31702
change Type to gobType.
fix some bugs around recursive structures.
lots of cleanup.
add the first cut at a type encoder.
R=rsc
DELTA=400 (287 added, 11 deleted, 102 changed)
OCL=31401
CL=31406