implements: initialize the internal package with minimal logging support

This log.go file establishes the ability for the package's user to hand
it any logger that meets the very minimal interface.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

contrib/implements/internal/implements/log.go

@@ -0,0 +1,20 @@
+package implements
+
+// DebugLogger is a simple interface to allow debug logging w/in the
+// implements package.
+type DebugLogger interface {
+	Printf(format string, v ...interface{})
+}
+
+// NoOpLogger is a dummy logger that generates no output.
+type NoOpLogger struct{}
+
+// Printf implements the DebugLogger interface.
+func (NoOpLogger) Printf(_ string, _ ...interface{}) {}
+
+var logger DebugLogger = NoOpLogger{}
+
+// SetLogger will set the given debug logger for the whole implements package.
+func SetLogger(l DebugLogger) {
+	logger = l
+}