Major refactoring for logging

[sangkeun00]

Please refer to #65 for details.

In addition, two comments I got during NeurIPS 2023 were:

• analog.update is too vague in that it's unclear what we are updating with this.
  • Solution: I changed the name to analog.setup. This way, it's more explicit that we are setting the configuration for logging.
• Currently, most our examples use analog as a name for the AnaLog instance, but this is confusing as our library name is also analog (we do import analog).
  • Solution: Inspired by wandb, we let users directly use analog after import by implementing basic (but most important) functionalities in __init__.py. With this, users can write their code as below:

import analog
from analog.analysis import InfluenceFunction

analog.init(project, config)
analog.watch(model)

for inputs, labels in data_loader:
    model.zero_grad()
    outs = model(inputs)
    loss = loss_fn(outs, labels)
    loss.backward()
    analog.log(data_id)

if_computer = analog.add_analysis(InfluenceFunction)
...

[sangkeun00]

While there can be some additional bugs in the refactored code, I was able to run major features without any errors. Therefore, I am merging this PR for now.