Suggestion: More uses for big file copy mode

[Deenayd]

Hello,

Some places where I think copying files with big buffers would be useful:
1. pack / unpack (with built in ZIP)
2. file split / combine
3. compare files by content
4. network copy (for local reads/writes)

It might be easier to create some kind of internal API for reads/writes which would switch to big buffers mode if enabled in the configuration. This API would be used everywhere where totalcmd accesses files.