Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/file/include_test.go

@@ -0,0 +1,32 @@
+package file
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+)
+
+// Make sure the external miekg/dns dependency is up to date
+
+func TestInclude(t *testing.T) {
+
+	name, rm, err := test.TempFile(".", "foo\tIN\tA\t127.0.0.1\n")
+	if err != nil {
+		t.Fatalf("Unable to create tmpfile %q: %s", name, err)
+	}
+	defer rm()
+
+	zone := `$ORIGIN example.org.
+@ IN SOA sns.dns.icann.org. noc.dns.icann.org. 2017042766 7200 3600 1209600 3600
+$INCLUDE ` + name + "\n"
+
+	z, err := Parse(strings.NewReader(zone), "example.org.", "test", 0)
+	if err != nil {
+		t.Errorf("Unable to parse zone %q: %s", "example.org.", err)
+	}
+
+	if _, ok := z.Search("foo.example.org."); !ok {
+		t.Errorf("Failed to find %q in parsed zone", "foo.example.org.")
+	}
+}