Add a makefile which builds by default and also has a clean target.

The clean function is justified because lack of an idiomatic way to
find and execute a clean target may have contributed to the error that that
previous commit addressed.

The use of a Makefile is justified by an idiomatic way to find and execute the clean function.

The use of the git ls-files is justified beccause of the need to exclude the one
source controlled file in package/lambda from cleanup.

Author: jonseymour

Makefile

@@ -0,0 +1,8 @@
+build:
+	./build-and-test.sh
+
+clean:
+	-rm -rf lambda/
+	-rm lambda-deploy.zip
+	-rm python/lambda-deploy.zip
+	git ls-files -o python/lambda | while read f; do rm -- "$$f"; done