Update supported versions

Improve doc generation

Update elixir version requirment to at least 0.15.0

* Require at least Elixir 0.14.1

* Fix Travis support

* Docs

* Hex support
* Travis support

* Improve reseting of tracer

* Make API more consistent
* Improve trace message printing
* Add Tests

Elixir 0.14.0 and 0.14.1 compatible release