Documentation Update and remove Spanish

Pulls in @individual61 's changes for the next release :sparkles: 

- update a huge amount of docs
- remove Spanish versions

Especially with the later one I am thinking about aiming for a `0.6.0` release instead of a `0.5.5` release since it "reduces" some functionality and changes the structure a bit more than just "fixing bugs" :)

Ok but on the other hand it's just "removing" files. Could be `0.5.5` anyway.

I wonne be pretty, too.

```c++
/************************* pngtest.cc ***************************
 *
 * ....
 */
```