Firebase-admin

* A new [`db`](https://godoc.org/firebase.google.com/go/db) package that facilitates basic data manipulation operations (create, read, update and delete), conditional updates (transactions) and advanced queries. Currently, this API does not support realtime event listeners.
* Updated all packages to import the standard `context` package available in golang1.7 and above.

`Firebase Cloud Messaging`

- A new [`messaging`](https://godoc.org/firebase.google.com/go/messaging) package for sending `messaging` messages and managing topic subscriptions.
- A new [`Send()`](https://godoc.org/firebase.google.com/go/messaging#Client.Send) function for sending `messaging` messages.
- A new [`SubscribeToTopic()`](https://godoc.org/firebase.google.com/go/messaging#Client.SubscribeToTopic) function for subscribing a list of device registration tokens to a `messaging` topic.
- A new [`UnubscribeFromTopic()`](https://godoc.org/firebase.google.com/go/messaging#Client.UnsubscribeFromTopic) function for unsubscribing a list of device registration tokens from a `messaging` topic.

`Firebase Auth`

- A new [`VerifyIDTokenAndCheckRevoked()`](https://godoc.org/firebase.google.com/go/auth#Client.VerifyIDToken) function to check for revoked ID tokens.
- A new [`RevokeRefreshTokens()`](https://godoc.org/firebase.google.com/go/auth#Client.RevokeRefreshTokens) function to invalidate all refresh tokens issued to a user.
- A new property `TokensValidAfterMillis` has been added to the [`auth.UserRecord`](https://godoc.org/firebase.google.com/go/auth#UserRecord) type.

Miscellaneous

* [chore] Release 2.4.1 Take 2 (388)
* Revert "[chore] Release 2.4.1 (386)" (387)
* [chore] Release 2.4.1 (386)
* (chore): Marked net 4.6.1 as deprecated (384)
* chore: Update integration test project setup instructions. (368)
* Update `github.ref` value in `release.yml` (367)
* New snippet with project id defined. (358)
* Uncomment the `Obsolete` tags for deprecated FCM batch send APIs (355)

New Features

* feat(fcm): Add `SendEachAsync` and `SendEachForMulticastAsync` for FCM batch send (348)

Miscellaneous

* [chore] Release 2.4.0 (354)
* Revert "[chore] Release 2.4.0 (350)" (353)
* [chore] Release 2.4.0 (350)

Miscellaneous

* [chore] Release 2.3.0 Take 2 (321)
* Revert "[chore] Release 2.3.0 (319)" (320)
* [chore] Release 2.3.0 (319)
* feat (fcm): Add additional Android Notification Parameters (317)
* chore: Build .net framework targets on linux (318)
* Update nightly.yml
* Update run_integration_tests.sh
* Update nightly.yml
* Update run_integration_tests.sh
* chore: Changing back to ubuntu-latest
* Rename run_integration_tests.ps1 to run_integration_tests.sh
* chore: switching to windows-latest
* chore: Install .NET Core SDKs explicitly
* Setup .NET Core
* Setup .NET Core on all platforms
* Switching nightly script back to windows-2019
* Changing nightly builds to use ubuntu-latest
* Set .NET core version in Nightly builds
* Revert "Add delayed response message for holidays (311)" (312)
* Add delayed response message for holidays (311)
* chore: Add nightly build workflow (305)

* Adding the `X-Client-Version` to the headers in the API calls for tracking API usage.