Setting version to 0.4.0:

This is a huge release, so here are only highlighted changes since the `v0.3.2`. See #9 and release notes for the `v0.4.0`-prereleases.

* New plugin integrations:
    - [sbt-taglist](https://github.com/johanandren/sbt-taglist): for warnings about `TODO` and `FIXME` tags
    - [sbt-github-release](https://github.com/ohnosequences/sbt-github-release): for automated release notes and artifacts on Github
    - [sbt-updates](https://github.com/rtimush/sbt-updates) plugin (#10): for warning about outdated dependencies

* Upgrades:
    - [sbt-release](https://github.com/sbt/sbt-release) -> 0.8.3
    - [sbt-s3-resolver](https://github.com/ohnosequences/sbt-s3-resolver) -> 0.11.0
    - [literator](https://github.com/laughedelic/literator) -> 0.5.1
    - [sbt-assembly](https://github.com/sbt/sbt-assembly) -> 0.11.2

* Improvements:
    - Split everithing on different modules
    - `clean` task now cleans `project/` folder from sbt-stuff
    - A _huge improvement_ of the release process (see #12 and docs)

version.sbt

@@ -1 +1 @@
-version in ThisBuild := "0.4.0-SNAPSHOT"
+version in ThisBuild := "0.4.0"