Doc: Running invoke as a library without Program

[LecrisUT]

Should document how one can run invoke not as a CLI program, for example to be run in a Jupyter notebook.

What I've found missing is:

• How to load configurations (as default invoke.yaml or overwritten prefixed my_module.yaml) using invoke search logic
• How to create a Context object, more specifically, so that it is compatible with other libraries that derive from it. E.g. Let's say we have two libraries: fabric defining ssh compatible context and another docker one.
  • We can have a logic select one context or the other based on values in invoke.yaml or a the config of the project, but then we would have to build one for each context
  • How could we combine contexts to have a docker-ssh, dynamically from the configuration or statically defining it manually
  • How to make the library by context independent so that the user can specify either fabric's ssh or the docker context without those becoming dependencies