relaxed library requirements

update to ecdsa 0.17.0

all tx i/o and scriptSig/pkscript sizes are now varint

updated version to 0.5.1

updated version to 0.5.1

fixed issue 9: empty lists as default args cause unexpected behavior

add method to check if address is bech32

import, comment and other cleanup

new version at 0.4.8

fixed rounding issue in to_satoshis method