Added statistical analysis tool (tool/stats)

Currently analyzes percentages of the following:
- version (how many 1.0 or 1.1)
- generator
- extension
- capability
- opcode prevalence
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 98cc771..430eb76 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -161,3 +161,4 @@
 
 add_subdirectory(opt)
 add_subdirectory(val)
+add_subdirectory(stats)