worked on the low-level setup code and Makefile some more

The Makefile now has separate lists for both output files and all kinds
of other nice features.

I think that the startup code actually copies the exception table into
RAM now.
diff --git a/bbb_cape/src/cape/bootloader.c b/bbb_cape/src/cape/bootloader.c
new file mode 100644
index 0000000..c429f38
--- /dev/null
+++ b/bbb_cape/src/cape/bootloader.c
@@ -0,0 +1,2 @@
+void _start(void) {
+}