Address().fromHashbuf() convenience method

...useful for when you have the pubkeyhash, but not the version byte.
Block parsing example

bitcoind saves blocks in files called blk*****.dat. Those files can be piped
into this example, which will parse them and spit out a nice looking string of
all the blocks, which also includes parsed transactions.
toJSON, fromJSON

Every object should have toJSON and fromJSON methods so you can have a reliable
way to store and retrieve objects.
update blockreader example to use toJSON