TOML File Support

[Yash-Agrawal10]

Adds support for documentation of both local and non-local functions using a sniff-test.toml file included at the root directory of a cargo project. Integrates with the newly simplified docstring parsing to support identical syntax to in-code sniff test documentation.

This is primarily done by creating an additional toml module within the annotations module, and passing around a TomlAnnotation object to functions that at some point need to check functions for docstrings, along with the already passed TyCtxt. If needed, we could later make a struct that encapsulates all the information needed to check functions for docstrings, but currently these are passed separately.

There are a few very brief tests included in tests/toml which demonstrate how the toml file works.