Express a clearer status about supported versions.

By explaining the full story in README.txt.
By inlining API 11 constants so we can really compile the library against API 4.

Change-Id: I423e807114c15805e97860ff5db22ef9ff1e24c0
diff --git a/library/Android.mk b/library/Android.mk
index 7d5cbb7..053084f 100644
--- a/library/Android.mk
+++ b/library/Android.mk
@@ -16,7 +16,7 @@
 
 include $(CLEAR_VARS)
 LOCAL_MODULE := android-support-multidex
-LOCAL_SDK_VERSION := 11
+LOCAL_SDK_VERSION := 4
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 
 ifneq "" "$(filter eng.%,$(BUILD_NUMBER))"