compression

Is your feature request related to a problem? Please describe.
When working with a big piece of text, I sometimes scroll down and copy some text into another tab. When switching back to the first tab, both the input and the output pane is back on top. So I don't know where I was working just now.

Describe the solution you'd like
After tab switching, scroll position should be remembere

the borg files cache can be rather large, because it keeps some information about all files that have been processed recently.

lz4 is a very fast compression / decompression algorithm, so we could try to use it to lower the in-memory footprint of the files cache entries.

before implementing this, we should check how big the savings typically are - to determine whether it is worthwhile doing

I've been treating tuShorten/tuWiden as a string-ish conversion between UTF16 and UTF 8, so I recommend this.

Here's the code; add it to the end of every tuShorten/tuWiden function.
if (out < (original_out + out_len)) out = 0;