Introduce dotted snippet names, enable loading all snippets, rework snippet-loading internals
Use much simpler caching mechanism for snippets.
Mandate using section name every time with 'use:' command
Empty yaml file is a valid assistant
Add argparse argument that allows parsing remainder of CL invocation as arguments for appendable snippets
Create a construct_arg class method for Argument, so that it's usable elsewhere
Revert "Add argparse argument that allows parsing remainder of CL invocation as arguments for appendable snippets"

This reverts commit aeca969fbbf2375de8fca900fe39edea15b30787.