add FilenamePrefixFilter

src/main/java/org/cobbzilla/util/io/FilenamePrefixFilter.java

@@ -0,0 +1,16 @@
+package org.cobbzilla.util.io;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+import java.io.File;
+import java.io.FilenameFilter;
+
+@AllArgsConstructor
+public class FilenamePrefixFilter implements FilenameFilter {
+
+    @Getter private final String prefix;
+
+    @Override public boolean accept(File dir, String name) { return name.startsWith(prefix); }
+
+}