vec: is_inlined -> not_inlined

If you allocate a vector on the stack and default initialise
it (i.e. {0}), then by default "is_inlined" = 0.  This is bad, as
technically speaking we should expect the vector to attempt to use
it's small inline buffer for vector operations before going onto the
heap - this will mess up our functions.  So here I adjust the name to
make default stack based allocation a bit easier.

alisp.h

@@ -66,7 +66,7 @@ typedef struct Vector
 {
   u64 size, capacity;
   // Small buffer optimisation
-  u8 is_inlined;
+  u8 not_inlined;
   union
   {
     void *ptr;