Implement folding properly

```
Folding is implemented in the function `hyperlight_calculate_fold_marks`
which is basically one big hack and only works and VB and C# `region` folds.

It's just a proof of concept at the moment. The code needs to be
refactored, cleaned up and proper handling for (several types of?)
language-independent folds needs to be added. Likewise, proper client-side
handling is needed (e.g. in the form of a `hyperlight_write_header` function).
```

Original issue reported on code.google.com by `konrad.r...@gmail.com` on 3 May 2009 at 3:15

Start by reading the hyperlight_calculate_fold_marks function described in the issue and trace how its fold marks reach the client. Define the supported language-independent fold cases and the client-side handling, then verify that folding works beyond the current VB and C# region support.

Written by the indexing model from the issue text.