Add pod and pod coverage tests.

Makefile.PL

@@ -22,4 +22,6 @@ $pkg->add_pm('lib/signatures.pm' => '$(INST_LIB)/signatures.pm');
 
 makemaker_args($pkg->get_makefile_vars);
 
+extra_tests();
+
 WriteAll;

xt/author/pod.t

@@ -0,0 +1,5 @@
+use strict;
+use warnings;
+use Test::Pod;
+
+all_pod_files_ok();

xt/author/podcoverage.t

@@ -0,0 +1,14 @@
+use strict;
+use warnings;
+use Test::Pod::Coverage;
+
+all_pod_coverage_ok({
+    also_private => [qw/
+        import
+        unimport
+        setup
+        setup_for
+        teardown
+        teardown_for
+    /],
+});