get this on hex as a pre-major

[vanderhoop]

let's get this out into the world:

• hex docs
• typespecs
• more examples of common use cases

[soonernotfaster]

Published a version of the framework on Hex. https://hexdocs.pm/exunit_elephant/0.1.0/Elephant.html It is clear that we need a more discoverable name, maybe ExMock?

Update: I have renamed the module to ExDoubles it's documentation is here: https://hex.pm/packages/exdoubles