Content paging compat + Load cursors in background.

Adds support for loading cursors in background.
Synthesize paged cursors from unpaged results when paging is requested.
Try to be more efficient than MatrixCursor: InMemoryCursor, avoids a lot of auto-boxing associated with building MatrixCursor.
Adds a very basic demo app that pages through content (but with buttons, not in response to scrolling).

Test: Added tests for new classes. They're awesome!
Change-Id: I024ee0d4a79b87816efd6ad8091bf6de7daf6995
diff --git a/content/Android.mk b/content/Android.mk
new file mode 100644
index 0000000..eff8215
--- /dev/null
+++ b/content/Android.mk
@@ -0,0 +1,29 @@
+# Copyright (C) 2017 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+LOCAL_USE_AAPT2 := true
+LOCAL_MODULE := android-support-content
+LOCAL_SDK_VERSION := $(SUPPORT_CURRENT_SDK_VERSION)
+LOCAL_SRC_FILES := $(call all-java-files-under, src)
+LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
+LOCAL_SHARED_ANDROID_LIBRARIES := \
+    android-support-compat \
+    android-support-annotations
+LOCAL_JAR_EXCLUDE_FILES := none
+LOCAL_JAVA_LANGUAGE_VERSION := 1.7
+LOCAL_AAPT_FLAGS := --add-javadoc-annotation doconly
+include $(BUILD_STATIC_JAVA_LIBRARY)