Revert "delete everything" (includes everything non-go-crypto)

This reverts commit 96a3502

lite/errors/errors_test.go

@@ -0,0 +1,18 @@
+package errors
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrorHeight(t *testing.T) {
+	e1 := ErrHeightMismatch(2, 3)
+	e1.Error()
+	assert.True(t, IsHeightMismatchErr(e1))
+
+	e2 := errors.New("foobar")
+	assert.False(t, IsHeightMismatchErr(e2))
+	assert.False(t, IsHeightMismatchErr(nil))
+}