docs/develop: More reorganization.

* There is now a 'busses' folder, and the extant USB/SDHCI/Bluetooth/etc.
   docs now live in it, instead of various other places.
 * kernel/ports is now kernel/arch, like it is in src/system.
   SPARC documentation is now in there, too.
 * VM files (these are rather outdated) are now in kernel/vm.
 * SCSI ASC info removed, this is easily available online and
   it doesn't seem to be very relevant.

docs/develop/kernel/vm/vm_store_null

@@ -0,0 +1,20 @@
+static void null_destroy(struct vm_store *store)
+	Frees this stores space.
+
+static off_t null_commit(struct vm_store *store, off_t size)
+	Sets committed size to size and returns it.
+
+static int null_has_page(struct vm_store *store, off_t offset)
+	returns 1.
+	
+static ssize_t null_read(struct vm_store *store, off_t offset, iovecs *vecs)
+	Returns -1.
+
+static ssize_t null_write(struct vm_store *store, off_t offset, iovecs *vecs)
+	Returns -1.
+
+static int null_fault(struct vm_store *store, struct vm_address_space *aspace, off_t offset)
+	Returns a Fatal page fault error.
+
+vm_store *vm_store_create_null(void)  	
+	Creates an empty vm_store struct.