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/org_writer_test.go

@@ -0,0 +1,65 @@
+package org
+
+import (
+	"fmt"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/pmezard/go-difflib/difflib"
+)
+
+func TestOrgWriter(t *testing.T) {
+	for _, path := range orgTestFiles() {
+		expected := fileString(path[:len(path)-len(".org")] + ".pretty_org")
+		reader, writer := strings.NewReader(fileString(path)), NewOrgWriter()
+		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)
+		}
+	}
+}
+
+func orgTestFiles() []string {
+	dir := "./testdata"
+	files, err := ioutil.ReadDir(dir)
+	if err != nil {
+		panic(fmt.Sprintf("Could not read directory: %s", err))
+	}
+	orgFiles := []string{}
+	for _, f := range files {
+		name := f.Name()
+		if filepath.Ext(name) != ".org" {
+			continue
+		}
+		orgFiles = append(orgFiles, filepath.Join(dir, name))
+	}
+	return orgFiles
+}
+
+func fileString(path string) string {
+	bs, err := ioutil.ReadFile(path)
+	if err != nil {
+		panic(fmt.Sprintf("Could not read file %s: %s", path, err))
+	}
+	return string(bs)
+}
+
+func diff(actual, expected string) string {
+	diff := difflib.UnifiedDiff{
+		A:        difflib.SplitLines(actual),
+		B:        difflib.SplitLines(expected),
+		FromFile: "Actual",
+		ToFile:   "Expected",
+		Context:  3,
+	}
+	text, _ := difflib.GetUnifiedDiffString(diff)
+	return text
+}