Improve what gets packaged into the tarball

The resulting tarball now includes the following additional files:

* MANIFEST.in
* Makefile
* UNLICENSE
* bin/check.sh
* bin/clean.sh
* bin/lint.sh
* bin/setup.sh
* bin/test.sh
* dev-environment.yml
* environment.yml
* tests/it/scripting.py

Author: ctrueden

MANIFEST.in

@@ -0,0 +1,19 @@
+# Metadata
+include MANIFEST.in
+include Makefile
+include README.md
+include UNLICENSE
+include pyproject.toml
+
+# Conda Environment Files
+include environment.yml
+include dev-environment.yml
+
+# Directory inclusion
+graft src
+graft tests
+graft bin
+
+# File exclusion
+global-exclude __pycache__
+global-exclude *.py[doc]