1. Use <stdbool.h> if it is available but keep a compatibility shim in
shared/defines.h in case it is not.
2. Unbreak the circular header dependencies (mostly):
2a. client.c and client.h may NOT depend on 'struct Menu'. Use a void pointer
and casts instead.
2b. Separate the data type definitions in client.h and screen.h from
function prototypes which may require other data structures. This makes
header dependencies much more easy to maintain. Usually the data types
should have been moved to their own files but I (mmdolze) chose to
separate them using different header guards.
2c. Remove many now unused header includes.
Apply (old BSD-) style on menuscreens.c.
mmdolze
a151ee0fc4