Clean-up exported API

Move functions in API to libnativehelper_api.h and retire macros
formerly in module_api.h.

Add doc comments methods in the API.

Move various C++ internal definitions to anonymous namespaces.

Bug: 123003088
Test: m
Change-Id: I216f13e2627f7f402b399bb96aec358ee127e4b9
diff --git a/include/nativehelper/toStringArray.h b/include/nativehelper/toStringArray.h
index 1965d6a..f716ac1 100644
--- a/include/nativehelper/toStringArray.h
+++ b/include/nativehelper/toStringArray.h
@@ -17,14 +17,7 @@
 #ifndef TO_STRING_ARRAY_H_included
 #define TO_STRING_ARRAY_H_included
 
-#include <stddef.h>
-
-#include <jni.h>
-#include "module_api.h"
-
-// Public API for libnativehelper library.
-MODULE_API jobjectArray newStringArray(JNIEnv* env, size_t count);
-MODULE_API jobjectArray toStringArray(JNIEnv* env, const char* const* strings);
+#include "libnativehelper_api.h"
 
 #ifdef __cplusplus