API Changelog 4.0.21 (linode#241)

* API Changelog 4.0.21

* Bump release/changelog dates

Author: nmelehan

content/changelog/2019/04-22-api.md

@@ -0,0 +1,24 @@
+---
+title: "4.0.21: 2019-04-22"
+date: "2019-04-22T08:00:00-04:00"
+description: "API Changelog 4.0.21"
+changelog:
+- API
+version: 4.0.21
+---
+
+### Added
+
+- Added taxes to invoices and invoice items.
+    - Added the *subtotal* and *tax* properties to invoices (GET /account/invoices/{invoiceId})
+    - The *total* property of an invoice now represents the total of the invoice after taxes.
+    - Added the *tax* and *total* properties to invoice items (GET /account/invoices/{invoiceId}/items).
+    - An invoice item's *total* is the item's *amount* plus the taxes levied on the item.
+- The Events endpoints (GET /account/events, GET /account/events/{eventId}) will now include Lassie reboots and reboots of a Linode's host.
+
+### Fixed
+
+- Reverted ability to filter StackScripts by image (introduced in release 4.0.19).
+- Resizing (POST /linode/instances/{linodeId}/resize) or upgrading (POST /linode/instances/{linodeId}/mutate) a Linode will now throw an error if there is no availability in the Linode's data center.
+- The *backups_enabled* property of a Linode will now return true if a Linode's backups are temporarily paused by the Linode Support Team.
+- Assigning a new credit card to an account (POST /account/credit-card) when the account has an expired credit card on file will no longer return an error.