Prep BCF for pypi upload.

* Refactored the BCF dir into a "src-layout" which I am more comfortable with. We can likely change this back if it is not compatible with other development

* I added a few setup files for the bcf package (setup.cfg, pyproject.toml and a MANIFEST.in file)

* Added two __init__.py files in the v2 and v3 subfolders for them to be picked up during package compilation

src/bcf/pyproject.toml

@@ -0,0 +1,12 @@
+[build-system]
+requires = [
+    "setuptools>=42",
+    "wheel"
+]
+build-backend = "setuptools.build_meta"
+
+[tool.black]
+line-length = 120
+
+[tool.isort]
+profile = "black"