Transaction: optional script for addInput
Transaction: simplify fromBuffer verbosity
add block.js and tests
bufferutils: add varIntBuffer
remove base58check

Use bs58check package solely from here on.
rename Message to message
crypto: remove Hmac* exposure in API
crypto: re-work fixtures for simplicity
HDNode: remove toBuffer/toHex
all: remove deprecated functionality
Wallet: fix impl. and tests after deprecated APIs removed
Transaction/TxBuilder: move all param coercion to TxBuilder