Add notes from #32 [ci skip]

HISTORY.md

@@ -1,4 +1,15 @@
+# HEAD
+
+* Tried to reduce the number of instances of respond_to? in the code by
+  pulling common uses of it out to methods. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+* The parse stack is now composed of simple objects instead of it being
+  an array of arrays. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+* Now using an identifier for an empty buffer instead of empty string. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+* Cleaned up several variables that were not being used. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+* Encapsulated stack so it's not being exposed as part of the API. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+* #cdata_block is now an alias instead of delegating to characters. [[#32](https://github.com/pauldix/sax-machine/pull/32)]
+
 # 0.1.0
 
-- rename parent to ancestor
-- added SAXMachine.configure
+* rename parent to ancestor
+* added SAXMachine.configure