Replace cborrpc.FixUpType() with mapstructure.
Replace cborrpc.FixUpType() with mapstructure.

Note that in principle this means we could skip a layer of indirection
in the RPC call implementations; instead of passing in map[string]interface{}
and then decoding those again, we could probably (assuming the byte-to-
string conversion works) directly pass in options structures.

diffeo/go-coordinate