literator v0.4.0 release

- [x] #1: language-agnostic
- [x] #4: fix bug
- [x] move index to the bottom
- [x] #7: better links: add links aliases to the bottom of each file
  ```
  text text [link in text][main/scala/SourceFile] text...
  ...
    [main/scala/SourceFile]: docs/src/main/scala/SourceFile.md
  ```

- [x] separate sub-projects for
  + library
  + command line tool
  + sbt-plugin