Move from flat layout approach to src layout

[xmnlab]

ref https://osl-incubator.github.io/scicookie/guide.html#project-layout

[xmnlab]

some discussions about this topic: https://github.com/osl-incubator/containers-sugar/issues/91

[xmnlab]

As you can see, there is no src folder. So, this is a flat layout, where typically source files are in a folder called with the same name of the package in the root of the project.

To convert that to src layout, basically:

1. Create a src folder in the root of the project
2. move makim to src
3. Update pyproject.toml

Verify in the code any place that is using the path containers_sugar/ and replace by the new path

Some references:

• https://github.com/arxlang/astx
• https://github.com/arxlang/astx/blob/main/pyproject.toml

[xmnlab]

completed by #63