Userland: Add a /bin/basename program.

Userland/basename.cpp

@@ -0,0 +1,12 @@
+#include <AK/FileSystemPath.h>
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        printf("usage: basename <path>\n");
+        return 1;
+    }
+    printf("%s\n", FileSystemPath(argv[1]).basename().characters());
+    return 0;
+}