There are certain RPCs where an address should be sent as the raw string
instead of the encoded bitcoin address since the RPC handler on the other
end expects "keys" instead of Bitcoin addresses.
For example, the multisignature RPCs addmultisigaddress and createmultisig
can work with pubkeys (compressed, uncompressed, or hybrid) as well as
Bitcoin addresses.
The original issue which prompted these changes was report by Paul Snow on
IRC.
Rather than using bytes.NewBuffer, which is a read/write entity
(io.ReadWriter), use bytes.NewReader which is only a read entitiy
(io.Reader). Benchmarking shows it's slightly faster and it's also
technically more accurate since it ensures the data is read-only.
There are several RPCs which accept a pointer to a hash, transaction,
block, etc. Previously not all RPCs handled being passed a nil pointer
consistently.
Closes#4.
