This was stupid as it prevented the compiler from doing code analysis
and discovering the bug leading to a segmentation fault when using
compiler optimization (see christian/shellipt#44).
Long overdue update of `README.md`.
* switching to recursive mutexes for now; easier to implement
* need to read user input from the window manager; hidden windows are
drawn when reading input from there
* note: occasional dead lock between PTY and ncurses mutex
* fixed type in class `SingleUserInput`
Christian Burger