Enhance Makefile with additional build targets and update Javadoc command to use Gradle wrapper

Author: jvmvik

Makefile

@@ -20,19 +20,22 @@ coverage:
 	./gradlew test jacocoTestReport
 	@echo "Coverage report: build/reports/jacoco/test/html/index.html"
 
+# Build the project
 build: clean
 	./gradlew build publishToMavenLocal -x test
 	@echo "see build/lib"
 
+# Build the demo project
 oobt: build
 	$(MAKE) -C demo all
 
 # Ruby must be installed (ERB is located under $GEM_HOME/bin or under Ruby installation)
 readme:
 	erb -T '-' README.md.erb > README.md
 
+# Build the javadoc
 doc:
-	gradle javadoc --info --warning-mode all
+	./gradlew javadoc --info --warning-mode all
 
 # Create a release using GitHub
 release: doc build