Prep for 5.x release

[DamonOehlman]

With #127 landing (ability to get extended search bot information) it's appropriate to release a new major version as it does change the behaviour of the bot attribute that can be returned from a detect() call.

These tasks need to be completed for me to feel comfortable with a 5.x release:

• Implement a discriminator for the various return types from a detect() call so that people can test result.type for what kind of result they have received. This is a pattern I personally prefer more but people will be able to use instanceof checks also to test for the different types. See add a type disciminator for the result #130.

• Update the README to outline the changes to the API