Add support for pyproject.toml

[novopl]

What?

Support reading peltak configuration from pyproject.toml. It should be possible to completely replace pelconf.yaml.

Why?

Looks like the python community is settling on the usage of pyproject.toml. This way we do not force a separate configuration file to exist in the project if the user chooses so. We should still support pelconf.yaml in case you want to keep the configuration separate (might be usefull for giant pyproject.toml files).

Added bonus is that even if the project is not using pelconf.yaml and has 0 peltak specific configuration in pyproject.toml we will still be able to use that file to determine the project root directory.

How?

We need to be able to read toml files. It is possible to store the existing configuration in toml format, so it's mainly creating a parser.

We also need a way to determine the project root directory by looking for pyproject.toml files as well.