Add callback for connects and reconnects.
Add custom/raw request/response support.
Add getinfo support.
Do not reissue rescan requests on reconnect.
Modify doco and example for btcwallet ws endpoint.
Correct a few cases of address encoding.

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.
Make golint happier.