Sync with new libtoxcore build system

First try to use pkg-config to find libtoxcore, fall back to manual
checks if pkg-config is not available.

Improve ncurses search, should now find everything on OSX.

src/friendlist.c

@@ -10,7 +10,7 @@
 #include <stdint.h>
 #include <ctype.h>
 
-#include "tox.h"
+#include <tox/tox.h>
 
 #include "friendlist.h"
 

src/main.c

@@ -25,7 +25,7 @@
 #include <sys/socket.h>
 #endif
 
-#include "tox.h"
+#include <tox/tox.h>
 
 #include "configdir.h"
 #include "toxic_windows.h"

src/toxic_windows.h

@@ -10,7 +10,7 @@
 #include <wctype.h>
 #include <wchar.h>
 
-#include "tox.h"
+#include <tox/tox.h>
 
 #define MAX_WINDOWS_NUM 32
 #define MAX_FRIENDS_NUM 100