Prepare README.md for github
u_mem: split memory debugging from NDEBUG
Compile out memory checker if not enabled
jukebox: avoid needless repeated strlen
gauges: fix use of snprintf

Pass the capacity of the buffer, not the expected number of bytes to
copy.
gauges: avoid needless strlen
menu: fix use of snprintf

Pass the capacity of the buffer, not the expected number of bytes to
copy.
net_udp: fix use of snprintf

Pass the capacity of the buffer, not the expected number of bytes to
copy.
songs: fix use of snprintf

Pass the capacity of the buffer, not the expected number of bytes to
copy.
physfsx: fix use of snprintf

Pass the capacity of the buffer, not the expected number of bytes to
copy.
Multiplayer: allow pausing in kmatrix screen
Build: respect $LDFLAGS
gauges: show players through walls, estimate distance
multi: hide unhandled /commands
net_udp: centralize UDP broadcast

Use a helper function to broadcast UDP packets to the IPv4 broadcast and
(if enabled) IPv6 multicast, so that callers do not need to handle both
at every call site.
args: reorder to avoid unaligned access
Add command line options to jump directly to multiplayer

Add -multiplayer-host, -multiplayer-join, and -multiplayer-find to jump
immediately to the multiplayer host/join/find submenus.  This is done
only once, so that the player can back out to the main menu.
Add -multiplayer-hidden to suppress game broadcasts
Mark some math as const correct
gauges: augment point display with vector data