isOpReturn

standard OP_RETURN scripts contain either just an OP_RETURN or an OP_RETURN
followed by a single pushdata OP with not more than 40 bytes.
stealth address to/from JSON
remove unused base58check dependency
remove unused addressString variable
allow bufs in constructors

For Transaction, Block and Blockheader. This is a convenience so if you happen
to have the buffer for one of these, you can make a new one like this:

Transaction(txbuf);

Rather than having to do this:

Transaction().fromBuffer(txbuf);
Key -> Keypair

...that is what is called everywhere else.
toJSON/fromJSON for privkey, pubkey, keypair
Stealthkey toJSON/fromJSON
extra curly braces for code readability
classify pubkeyhash and scripthash scripts

...both the "in" (ScriptSig) and "out" (ScriptPubkey)