This makes several largely unrelated improvements in the high-level API
and in the README.
Main improvements in high-level API:
* Improve naming in trainer-related abstractions, moved some classes
from examples to the library
* Improve environment factory abstraction
* Some bug-fixes
Main changes in README:
* Add high-level example and update procedural/low-level example
* Improve language/wording
6e1ffe58e5