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 am running out of strange comments. let's put
```c++
/******* pngtest.cc ****
 *
 * ....
 */
```

here too ;)