#98 Increase granularity of context.

[alexanderlazarev0]

Implements #98

Split context into:

• global context
• resource specific contexts (1 per ContextResource)

API changes:

All API changes only come in the form of extending current functionality via methods or optional arguments. Except for:

To set the global_context when calling container_context(), one needs to explicitly pass it as a keyword arguments.

Instead of:

initial_context = {}
async with container_context(initial_context):
    ...

Now one must use:

initial_context = {}
async with container_context(initial_context=initial_context):
    ...

This makes the new API incompatible with the current version!
-> Hence, my suggestion is to release this with 2.0

Points of discussion:

I will leave comments to be discusses in this pull request.

Still TODO:

• Implement discussion changes.
• Extend documentation.

Implementation notes:

@lesnik512 I did some test approaches prior to this implementation. Keeping one contextvars.ContextVar for all ContextResources and modifying the dict is not really feasible since you would need to deepcopy() the dict and its contents to the newly created context. In that case, one would need to look for a different solution from contextvars.