Rename some variables for more clarity.

No functional change.

Resolves #131

src/misc.h

@@ -46,7 +46,7 @@ namespace Time {
 template<class Entry, int Size>
 struct HashTable {
   HashTable() : table(Size, Entry()) {}
-  Entry* operator[](Key k) { return &table[(uint32_t)k & (Size - 1)]; }
+  Entry* operator[](Key key) { return &table[(uint32_t)key & (Size - 1)]; }
 
 private:
   std::vector<Entry> table;