Block-io

This release fixes a packaging issue on PyPi.

This release features:
- Better error handling with specific Exception classes
- Relegation of specific package versions to requirements.txt
- Update dependency ecdsa to 0.13
- Update tests.py to use updated ecdsa deterministic signature interface

Added support for sweeping legacy addresses (uncompressed keys).

This release adds a sweep functionality. You can now provide a Private Key to sweep coins (transfer) from a source address into a destination address.

_Usage_:

`block_io.sweep_from_address(from_address='SOURCE ADDRESS',private_key='WALLET IMPORT FORMAT PRIVATE KEY FOR SOURCE ADDRESS',to_address='DESTINATION ADDRESS TO DEPOSIT COINS INTO')`

Significant changes:
- Add BIP62 compliant low 's' in ECDSA signatures, see https://github.com/bitcoin/bips/blob/master/bip-0062.mediawiki#low-s-values-in-signatures

Python library for Block.io's API v2 support. Now includes MultiSig client-side signatures for security.