mention the GTA (get-async) and GTO (get-offset) commands
fixed some bugs introduced with last changes (asynchronous-reading)

+ some cleanings
support the GTA command and various fixes to the asynchronous-reading implementation

was still untested .. many small things have been tested while testing
fixed the asynchronous-reading implementation while testing

many small things were missing or wrong
updated libiomux

major fix for epoll/kqueue implementation, it was leaking the epoll/kqueue fd
when the mux was destroyed. It was unnoticed so far because we were allocating
one mux per workers which would have lived until the end of the program.
Now that the asynchronous readers create iomuxes on the fly the fd leakage was
immediately noticed