Add changelog for 3.0.0-alpha2 release.

Change-Id: I4cbb3374e351c31611de472c7d5d78e4ce2b0f3b

CHANGES.txt

+2015-2-22 version 3.0.0-alpha-2 (Ruby/JavaNano):
+  General
+  * Introduced two new language implementations (Ruby and JavaNano) to proto3.
+  * Various bug fixes since 3.0.0-alpha-1
+
+  Ruby:
+    TODO(cfallin): Add descriptions here.
+
+  JavaNano:
+    JavaNano is a special code generator and runtime library designed especially
+    for resource-restricted systems, like Android. It is very resource-friendly
+    in both the amount of code and the runtime overhead. Here is an an overview
+    of JavaNano features compared with the official Java protobuf:
+
+    - No descriptors or message builders.
+    - All messages are mutable; fields are public Java fields.
+    - For optional fields only, encapsulation behind setter/getter/hazzer/
+      clearer functions is opt-in, which provide proper 'has' state support.
+    - For proto2, if not opted in, has state (field presence) is not available.
+      Serialization outputs all fields not equal to their defaults.
+      The behavior is consistent with proto3 semantics.
+    - Required fields (proto2 only) are always serialized.
+    - Enum constants are integers; protection against invalid values only
+      when parsing from the wire.
+    - Enum constants can be generated into container interfaces bearing
+      the enum's name (so the referencing code is in Java style).
+    - CodedInputByteBufferNano can only take byte[] (not InputStream).
+    - Similarly CodedOutputByteBufferNano can only write to byte[].
+    - Repeated fields are in arrays, not ArrayList or Vector. Null array
+      elements are allowed and silently ignored.
+    - Full support for serializing/deserializing repeated packed fields.
+    - Support  extensions (in proto2).
+    - Unset messages/groups are null, not an immutable empty default
+      instance.
+    - toByteArray(...) and mergeFrom(...) are now static functions of
+      MessageNano.
+    - The 'bytes' type translates to the Java type byte[].
+
+    See javanano/README.txt for details.
+
 2014-12-01 version 3.0.0-alpha-1 (C++/Java):
 
   General

javanano/README.txt

@@ -68,18 +68,20 @@ running unit tests.
 Nano version
 ============================
 
-Nano is a special code generator and runtime library designed specially
-for Android, and is very resource-friendly in both the amount of code
-and the runtime overhead. An overview of Nano features:
+JavaNano is a special code generator and runtime library designed specially for
+resource-restricted systems, like Android. It is very resource-friendly in both
+the amount of code and the runtime overhead. Here is an overview of JavaNano
+features compared with the official Java protobuf:
 
 - No descriptors or message builders.
 - All messages are mutable; fields are public Java fields.
 - For optional fields only, encapsulation behind setter/getter/hazzer/
   clearer functions is opt-in, which provide proper 'has' state support.
-- If not opted in, has state is not available. Serialization outputs
-  all fields not equal to their defaults (see important implications
-  below).
-- Required fields are always serialized.
+- For proto2, if not opted in, has state (field presence) is not available.
+  Serialization outputs all fields not equal to their defaults
+  (see important implications below).
+  The behavior is consistent with proto3 semantics.
+- Required fields (proto2 only) are always serialized.
 - Enum constants are integers; protection against invalid values only
   when parsing from the wire.
 - Enum constants can be generated into container interfaces bearing
@@ -88,8 +90,8 @@ and the runtime overhead. An overview of Nano features:
 - Similarly CodedOutputByteBufferNano can only write to byte[].
 - Repeated fields are in arrays, not ArrayList or Vector. Null array
   elements are allowed and silently ignored.
-- Full support of serializing/deserializing repeated packed fields.
-- Support of extensions.
+- Full support for serializing/deserializing repeated packed fields.
+- Support  extensions (in proto2).
 - Unset messages/groups are null, not an immutable empty default
   instance.
 - toByteArray(...) and mergeFrom(...) are now static functions of
@@ -200,7 +202,7 @@ optional_field_style={default,accessors,reftypes} (default: default)
 
   In the default style, optional fields translate into public mutable
   Java fields, and the serialization process is as discussed in the
-  "IMPORTANT" section above. 
+  "IMPORTANT" section above.
 
   * accessors *