pspg has menu

The pager pspg has more than 30 keyboard short cuts, what can be hard to use for beginners without Linux command line knowleadge.

For this reason I enhanced pspg about menus. Unfortunately I didn't find any library that implements menu on ncurses platform. Native ncurses menus doesn't support mouse well, and has little bit different philosophy than CUA. So I wrote own st-menu library. This library is available for generic and free usage. pspg can be use as referential usage of this library.

Few screenshots: