Define a LH_LOAD_FACTOR constant and note the range that it can be set to.

Change the resize check from "count > size" to "count >= size" to avoid a
potential infinite loop with high load factors and a full hash table.

linkhash.h

@@ -21,6 +21,13 @@ extern "C" {
  */
 #define LH_PRIME 0x9e370001UL
 
+/**
+ * The fraction of filled hash buckets until an insert will cause the table
+ * to be resized.  
+ * This can range from just above 0 up to 1.0.
+ */
+#define LH_LOAD_FACTOR 0.66
+
 /**
  * sentinel pointer value for empty slots
  */