Enumerate exercises and add 'Solution' headings

001_leap_year.lua

@@ -1,5 +1,7 @@
+-- Solution --------------------------------------------------------------------
+
 function leap_year(year)
-   -- Your solution here
+   -- Your implementation here
 end
 
 -- Tests -----------------------------------------------------------------------

002_resistor_colours.lua

@@ -1,3 +1,5 @@
+-- Solution --------------------------------------------------------------------
+
 -- Give the colours whatever values are convenient
 black = undefined
 brown = undefined
@@ -13,7 +15,7 @@ gold = undefined
 silver = undefined
 
 function decode_resistance(colours)
-   -- Your solution here
+   -- Your implementation here
 end
 
 -- Tests -----------------------------------------------------------------------

003_hamming_distance.lua

@@ -1,5 +1,7 @@
+-- Solution --------------------------------------------------------------------
+
 function hamming_distance(str1, str2)
-   -- Your solution here
+   -- Your implementation here
 end
 
 -- Tests -----------------------------------------------------------------------