Move Python source to subdirectory.

This allows testing versions not built in-place. Otherwise
importing (or testing) in the package root fails without develop
builds.
Replace maturin with setuptools_rust since maturin fails with
proper project structure.

.github/workflows/python.yml

@@ -114,6 +114,6 @@ jobs:
         run: |
           python -m venv .env
           source .env/bin/activate
-          pip install pytest requests maturin
+          pip install pytest requests setuptools_rust 
-          maturin develop --release
+          python setup.py develop
           make test

bindings/python/Makefile

@@ -2,11 +2,11 @@
 
 # Format source code automatically
 style:
-	black --line-length 100 --target-version py35 examples tokenizers tests
+	black --line-length 100 --target-version py35 examples py_src/tokenizers tests
 
 # Check the source code is formatted correctly
 check-style:
-	black --check --line-length 100 --target-version py35 examples tokenizers tests
+	black --check --line-length 100 --target-version py35 examples py_src/tokenizers tests
 
 # Launch the test suite
 test:

bindings/python/setup.py

@@ -31,6 +31,7 @@ setup(
         "Programming Language :: Python :: 3.8",
         "Topic :: Scientific/Engineering :: Artificial Intelligence",
     ],
+    package_dir={"": "py_src"},
     packages=[
         "tokenizers",
         "tokenizers.models",