fastlane 2.0

_fastlane_ 2.0

From now on, all of _fastlane_ is inside the _fastlane_ gem :tada: This will enable us to be a lot faster and more efficient in the future :rocket:

- If you run some tools directly without _fastlane_, please run `fastlane [tool]` instead of `[tool]` (e.g. `fastlane gym ...`). If you don't prefix your commands, the old version of the tool will be used. Using the tool's name directly is now deprecated.
- If you have a `Gemfile`, update it to just include `gem "fastlane"`, and not any of the other tools any more
- As a plugin maintainer, make sure to remove dependencies to _spaceship_ and _fastlane_core_ (I submitted PRs to all public plugins for that this was the case)

- Make releases much simpler, just one gem to ship
- No more internal dependency updates
- No more version conflicts if we add some methods to some sub-gems
- 1 PR could modify multiple tools and tests are still passing (does not mean we have to, but we can for example to update _spaceship_ and _deliver_ at the same time if necessary)

https://github.com/fastlane/fastlane/releases/tag/2.0.0
