add window captions.

...and reindent.
split not-essential core code into aux lib.

the aux library offers not-absolutely-critical rendering
code like stock object creation and text handling.
Still built and shipped by default (no extra deps).
compile plush only on request.

the plush 1.2.x vanilla code is not expected to change,
so it make no sense to build it over and over again by default.
If you want plush, there are separate repos always available,
and of course a build option :)