Added an apple2enh specific linker configuration file and made use of it in the apple2enh build.

The new linker configuration file:
- Defines interruptors
- Uses language card bank2 memory from D000-D3FFF. This overwrites the ProDOS 8 quit code. Thus quitting Contiki via Ctrl-Reset now chrashes! I'll take care of that with subsequent changes...
diff --git a/contiki-apple2/apple2enh.cfg b/contiki-apple2/apple2enh.cfg
new file mode 100644
index 0000000..0286a5a
--- /dev/null
+++ b/contiki-apple2/apple2enh.cfg
@@ -0,0 +1,39 @@
+MEMORY {
+    ZP:     start = $0080, size = $001A, file = "", define = yes;
+    BUFFER: start = $0800, size = $0400, file = "";
+    HEADER: start = $0000, size = $0004, file = "contiki";
+    RAM:    start = $0C00, size = $8A00, file = "contiki";
+    PIC:    start = $0000, size = $FFFF, file = "contiki";
+    TMP:    start = $0000, size = $FFFF, file = "contiki";
+    LC:     start = $D000, size = $1000, file = "contiki";
+}
+SEGMENTS {
+    ZEROPAGE: load = ZP,             type = zp;
+    UIPBUF:   load = BUFFER,         type = bss;
+    EXEHDR:   load = HEADER,         type = ro;
+    STARTUP:  load = RAM,            type = ro,  define = yes;
+    CONTIKI:  load = RAM,            type = ro;
+    RODATA:   load = RAM,            type = ro;
+    DATA:     load = RAM,            type = rw;
+    BSS:      load = RAM,            type = bss, define = yes;
+    BOOT:     load = PIC,            type = ro,  define = yes;
+    INIT:     load = TMP, run = RAM, type = ro,  define = yes;
+    CODE:     load = LC,             type = ro,  define = yes;
+}
+FEATURES {
+    CONDES: segment = INIT,
+	    type  = constructor,
+	    label = __CONSTRUCTOR_TABLE__,
+	    count = __CONSTRUCTOR_COUNT__;
+    CONDES: segment = RODATA,
+	    type  = destructor,
+	    label = __DESTRUCTOR_TABLE__,
+	    count = __DESTRUCTOR_COUNT__;
+    CONDES: segment = RODATA,
+	    type  = interruptor,
+	    label = __INTERRUPTOR_TABLE__,
+	    count = __INTERRUPTOR_COUNT__;
+}
+SYMBOLS {
+    __STACKSIZE__ = $200;
+}