0.1.0

Added

• Add ReqSSRF.attach/2, which checks every hop of a Req request and halts
  it with ReqSSRF.BlockedError if the URL may not be fetched.
• Add ReqSSRF.check/2 and ReqSSRF.allowed?/2 for validating a single URL,
  and ReqSSRF.public_address?/1 for a single IP address.