Python: CG trace: Move code to src/

As recommended in https://blog.ionelmc.ro/2014/05/25/python-packaging/ and
following pattern of black and pytest

python/tools/recorded-call-graph-metrics/.gitignore

@@ -2,6 +2,6 @@
 cg-trace-example-db/
 
 # Artifact from building `pip install -e .`
-cg_trace.egg-info/
+src/cg_trace.egg-info/
 
 venv/

python/tools/recorded-call-graph-metrics/README.md

@@ -40,7 +40,10 @@ After following setup instructions below, run the `recreate-db.sh` script to cre
           "editor.codeActionsOnSave": {
               "source.organizeImports": true
           }
-      }
+      },
+      "python.autoComplete.extraPaths": [
+          "src"
+      ]
   }
   ```
 

python/tools/recorded-call-graph-metrics/setup.py

@@ -1,16 +1,14 @@
 from setuptools import find_packages, setup
 
-from cg_trace import MIN_PYTHON_VERSION_FORMATTED, __version__
-
-# TODO: There was some benefit of structuring your code as `src/yourpackage/code.py`
-# instead of `yourpackage/code.py` concerning imports, but I don't recall the details
+# using src/ folder as recommended in: https://blog.ionelmc.ro/2014/05/25/python-packaging/
 
 setup(
     name="cg_trace",
-    version=__version__,
+    version="0.0.1",
     description="Call graph tracing",
-    packages=find_packages(),
+    packages=find_packages("src"),
+    package_dir={"": "src"},
     install_requires=["lxml"],
     entry_points={"console_scripts": ["cg-trace = cg_trace.main:main"]},
-    python_requires=">={}".format(MIN_PYTHON_VERSION_FORMATTED),
+    python_requires=">=3.6",
 )