diff --git a/bump-api-library/ant.properties b/bump-api-library/ant.properties
deleted file mode 100644
index ee52d86..0000000
--- a/bump-api-library/ant.properties
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file is used to override default values used by the Ant build system.
-#
-# This file must be checked in Version Control Systems, as it is
-# integral to the build system of your project.
-
-# This file is only used by the Ant script.
-
-# You can use this to override default values such as
-#  'source.dir' for the location of your java source folder and
-#  'out.dir' for the location of your output folder.
-
-# You can also use it define how the release builds are signed by declaring
-# the following properties:
-#  'key.store' for the location of your keystore and
-#  'key.alias' for the name of the key to use.
-# The password will be asked during the build when you use the 'release' target.
-
diff --git a/bump-api-library/build.xml b/bump-api-library/build.xml
index 02f6167..fddecf7 100644
--- a/bump-api-library/build.xml
+++ b/bump-api-library/build.xml
@@ -4,7 +4,7 @@
     <!-- The local.properties file is created and updated by the 'android' tool.
          It contains the path to the SDK. It should *NOT* be checked into
          Version Control Systems. -->
-    <loadproperties srcFile="local.properties" />
+    <property file="local.properties" />
 
     <!-- The ant.properties file can be created by you. It is only edited by the
          'android' tool to add properties to it.
@@ -28,6 +28,15 @@
          -->
     <property file="ant.properties" />
 
+    <!-- if sdk.dir was not set from one of the property file, then
+         get it from the ANDROID_HOME env var.
+         This must be done before we load project.properties since
+         the proguard config can use sdk.dir -->
+    <property environment="env" />
+    <condition property="sdk.dir" value="${env.ANDROID_HOME}">
+        <isset property="env.ANDROID_HOME" />
+    </condition>
+
     <!-- The project.properties file is created and updated by the 'android'
          tool, as well as ADT.
 
@@ -41,25 +50,23 @@
 
     <!-- quick check on sdk.dir -->
     <fail
-            message="sdk.dir is missing. Make sure to generate local.properties using 'android update project'"
+            message="sdk.dir is missing. Make sure to generate local.properties using 'android update project' or to inject it through the ANDROID_HOME environment variable."
             unless="sdk.dir"
     />
 
-
-<!-- extension targets. Uncomment the ones where you want to do custom work
-     in between standard targets -->
-<!--
-    <target name="-pre-build">
-    </target>
-    <target name="-pre-compile">
-    </target>
-
-    /* This is typically used for code obfuscation.
-       Compiled code location: ${out.classes.absolute.dir}
-       If this is not done in place, override ${out.dex.input.absolute.dir} */
-    <target name="-post-compile">
-    </target>
--->
+    <!--
+        Import per project custom build rules if present at the root of the project.
+        This is the place to put custom intermediary targets such as:
+            -pre-build
+            -pre-compile
+            -post-compile (This is typically used for code obfuscation.
+                           Compiled code location: ${out.classes.absolute.dir}
+                           If this is not done in place, override ${out.dex.input.absolute.dir})
+            -post-package
+            -post-build
+            -pre-clean
+    -->
+    <import file="custom_rules.xml" optional="true" />
 
     <!-- Import the actual build file.
 
diff --git a/bump-api-library/proguard-project.txt b/bump-api-library/proguard-project.txt
new file mode 100644
index 0000000..f2fe155
--- /dev/null
+++ b/bump-api-library/proguard-project.txt
@@ -0,0 +1,20 @@
+# To enable ProGuard in your project, edit project.properties
+# to define the proguard.config property as described in that file.
+#
+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in ${sdk.dir}/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the ProGuard
+# include property in project.properties.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# Add any project specific keep options here:
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}