Add a UUID module to btcore for operating on UUIDs.

This change only adds a single function, uuid_is_empty, but I expect
other UUID-related functions to find themselves here.
diff --git a/btcore/Android.mk b/btcore/Android.mk
index d530655..ce00814 100644
--- a/btcore/Android.mk
+++ b/btcore/Android.mk
@@ -24,7 +24,8 @@
     $(LOCAL_PATH)/include
 
 LOCAL_SRC_FILES := \
-    src/bdaddr.c
+    src/bdaddr.c \
+    src/uuid.c
 
 LOCAL_CFLAGS := -std=c99 $(bdroid_CFLAGS)
 LOCAL_MODULE := libbtcore