Use in-memory, on-disk-backed DB

- removed sqlite
- added stubs for MemDB
- removed sqlite3 vendor

Fixes #7

Change-Id: I97b7f274be8db5ff02d9a4e4b8f616403fd6313a

testing.go

@@ -7,25 +7,21 @@ import (
 	"testing"
 )
 
-func testDB(t *testing.T) (*DB, func()) {
+// TestDB returns a populated MemDB in a temp location, as well as a function
+// to call at cleanup time.
+func TestDB(t *testing.T) (*MemDB, func()) {
 	dir, err := ioutil.TempDir("", "vain-testing-")
 	if err != nil {
 		t.Fatalf("could not create tmpdir for db: %v", err)
 		return nil, func() {}
 	}
-	name := filepath.Join(dir, "test.db")
-	db, err := NewDB(name)
+	name := filepath.Join(dir, "test.json")
+	db, err := NewMemDB(name)
 	if err != nil {
 		t.Fatalf("could not create db: %v", err)
 		return nil, func() {}
 	}
-
-	if err := db.Init(); err != nil {
-		return nil, func() {}
-	}
-
 	return db, func() {
-		db.Close()
 		if err := os.RemoveAll(dir); err != nil {
 			t.Fatalf("could not clean up tmpdir: %v", err)
 		}