Rename files containing org and htm writer

The naming `org.go` is confusing as it's not the main class of the org package

org/html_writer_test.go

@@ -0,0 +1,23 @@
+package org
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestHTMLWriter(t *testing.T) {
+	for _, path := range orgTestFiles() {
+		expected := fileString(path[:len(path)-len(".org")] + ".html")
+		reader, writer := strings.NewReader(fileString(path)), NewHTMLWriter()
+		actual, err := NewDocument().Silent().SetPath(path).Parse(reader).Write(writer)
+		if err != nil {
+			t.Errorf("%s\n got error: %s", path, err)
+			continue
+		}
+		if actual != expected {
+			t.Errorf("%s:\n%s'", path, diff(actual, expected))
+		} else {
+			t.Logf("%s: passed!", path)
+		}
+	}
+}