Add alpha and numeric keyed Hash workloads

Set the env var `N` to specify the size of the Hash to test. For
example, in a Windows CMD.EXE:

  for %I in (1,2) do @set N=%I && @echo N=%I && rci bench core_hash_num_size_N

workloads/core_hash_alpha_size_N.rb

@@ -0,0 +1,13 @@
+c = (ENV['MEASURE_EXTENDED'] || 1).to_i
+
+# set env var `N` to desired Hash size to test
+n = (ENV['N'] || 6).to_i
+
+k = 'aaa'
+c.times do
+  500_000.times do
+    h = {}
+    n.times { h[k] = true; h[k]; k = k.succ }
+    h.each { |k,_| h[k] = h[k] }
+  end
+end

workloads/core_hash_num_size_N.rb

@@ -0,0 +1,12 @@
+c = (ENV['MEASURE_EXTENDED'] || 1).to_i
+
+# set env var `N` to desired Hash size to test
+n = (ENV['N'] || 6).to_i
+
+c.times do
+  500_000.times do
+    h = {}
+    n.times { |i| h[i] = true; h[i] }
+    h.each { |k,_| h[k] = h[k] }
+  end
+end