🌈 sessions were re-written, update to 4.0.0-alpha.2, read HISTORY.md

**Sessions were re-written **

- Developers can use more than one 'session database', at the same time,
to store the sessions
- Easy to develop a custom session database (only two functions are
required (Load & Update)), [learn
more](https://github.com/iris-contrib/sessiondb/blob/master/redis/database.go)
- Session databases are located
[here](https://github.com/iris-contrib/sessiondb), contributions are
welcome
- The only frontend deleted 'thing' is the: **config.Sessions.Provider**
- No need to register a database, the sessions works out-of-the-box
- No frontend/API changes except the
`context.Session().Set/Delete/Clear`, they doesn't return errors
anymore, btw they (errors) were always nil :)
- Examples (master branch) were updated.

```sh
$ go get github.com/iris-contrib/sessiondb/$DATABASE
```

```go
db := $DATABASE.New(configurationHere{})
iris.UseSessionDB(db)
```

> Note: Book is not updated yet, examples are up-to-date as always.

README.md

@@ -145,7 +145,7 @@ I recommend writing your API tests using this new library, [httpexpect](https://
 Versioning
 ------------
 
-Current: **v4.0.0-alpha.1**
+Current: **v4.0.0-alpha.2**
 
 >  Iris is an active project
 
@@ -157,7 +157,7 @@ Todo
 > for 'v4'
 
 - [x] Refactor & extend view engine, separate the engines from the main code base, easier for the community to create new view engines
-- [ ] Refactor & extend sessions, split the providers and stores to the iris-contrib
+- [x] Refactor & extend sessions, split the different databases functionality to the iris-contrib
 - [ ] Refactor & extends the rest render engine in order to be able to developer to use their own implemention for rendering restful types, like, for example a  custom JSON implementation using no-standard go package for encode/decode
 - [ ] Move the iris/websocket package's source code inside iris/websocket.go one file, to be easier to use by users without import a new package
 - [ ] configs package should be removed after all these, we will not need big configurations because of different packages splitted & moved to the iris-contrib, we will keep interfaces and all required things inside kataras/iris.go.
@@ -192,7 +192,7 @@ License can be found [here](LICENSE).
 [Travis]: http://travis-ci.org/kataras/iris
 [License Widget]: https://img.shields.io/badge/license-MIT%20%20License%20-E91E63.svg?style=flat-square
 [License]: https://github.com/kataras/iris/blob/master/LICENSE
-[Release Widget]: https://img.shields.io/badge/release-v4.0.0--alpha.1-blue.svg?style=flat-square
+[Release Widget]: https://img.shields.io/badge/release-v4.0.0--alpha.2-blue.svg?style=flat-square
 [Release]: https://github.com/kataras/iris/releases
 [Chat Widget]: https://img.shields.io/badge/community-chat-00BCD4.svg?style=flat-square
 [Chat]: https://kataras.rocket.chat/channel/iris