Prepare for 2.3.0 release.

CHANGELOG.md

-# Changes in version 2.3.0 - 2018-0?-??
+# Changes in version 2.3.0 - 2018-04-18
 
  * Medium changes
    - Replace ServerDescriptor#getHiddenServiceDirVersions with

build.xml

@@ -6,7 +6,7 @@
 
 <project default="usage" name="metrics-lib" basedir=".">
 
-  <property name="release.version" value="2.2.0-dev" />
+  <property name="release.version" value="2.3.0" />
   <property name="javadoc-title" value="Tor Metrics Library API Documentation"/>
   <property name="javadoc-excludes" value="**/impl/** **/index/** **/internal/** **/log/**" />
   <property name="implementation-title" value="Tor Metrics Library" />