Release 7.0.0

• Shouldn't throw on response error
• Fix retries not respected properly
• Respect Retry-After header
• Create a class for the default Agent so that the agents won't be
  shared globally as that might be unexpected
• Fix Agent defaults
• Move redirect handling into a separate file to allow better
  test coverage
• Fix IP caching and fetching using IP addresses
• Do not modify the original opts object
• Allow redirect opt like in node-fetch
• Set our own user-agent