Your comments

This will be in the next version after Textastic 3.2.
I've finally hand a look at the crash reports. The problem happens when remote file listings are parsed. I've already changed this particular part of the code so it should be fixed in the next version.
Did you try to organize your files in folders instead? What's missing for you?
I don't want to publish numbers, but I'm happy with the amount of copies sold. More would probably cause too much support. I could live off of the sales of Textastic alone, but I have another popular app in Germany ("Rezepte") and a few apps I did with a business partner ("The Photo Cookbook", "History of Rock"...). So the App Store works if you are just a single developer and you know how to create great apps.
I'll consider it. I'm not sure if it can be persisted to flash memory but I'll try.
The undo history is cleared in two cases:
  • when you switch a file
  • when the iPad is running out of memory and requesting apps to free memory

I guess the second case is what happened in your case.

Yes, you can upload any type of file. 

If you want to know how to get pictures into Textastic from the Photos app, have a look at the comments in http://feedback.textasticapp.com/topic/9278-import-pictures-from-the-photos-app/ to see how you can do this with the Dropbox app.
How did you create the symlink? Do you have a jailbroken device?