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

removed segwit marker for segwit non-signed transactions

fixed utils import

added utils module with decimal8 method plus minor cleanup

updated docs and tagged to 0.4.3 for pypi