Main Changes

We realized that "environments" was a concept that was not easy to grasp so we renamed it to "context", which seems to fit more with "a value that is constant throughout compositions".

We renamed every instance of environment to context, including EnvironmentError - which is now ContextError -, and isEnvironmentError to isContextError.
The legacy functions and classes are deprecated but this change shouldn't be breaking as we only plan to get rid of them at v5.