"Private" helper library Util name clashing

[soren-n]

Apparently the package stanza does not result in private libraries being actually private.
This is because the name is not mangled to become unique and tied to the project, and so will name clash with other libraries with the same name in the global context.

But it looks like this behaviour is on its way:
ocaml/dune#3864

To patch this for now; I'll mangle the name Util manually to Typeset_util.
I'll leave this issue open until the dune issue is resolved; then I'll de-mangle Typeset_util back to Util.

The reason for me insisting on the separation; Having the helper sources and library sources separate in a project structure, makes the project easier to maintain; since it is easier to understand when there is a practical separation of concerns.

Also to avoid code duplication; in this project both lib, test and example depend on util.

[soren-n]

Move Util out into its own package since it was using copies of it for other projects; github.com/soren-n