A wrapper of Android Storage Access Framework for writing files on Ext SD card in both Java and JNI native code.

Use DocumentFile for Java code to write,
and xhook to hook native code (such as fopen, mkdir, remove),
so that the native code can use SAF to write file.

[Java usage]

See `SafFile.java' in detail.

1. Use requestDocUri to get the docUri, and use saveDocUriFromResult in onActivityResult to save the docUri in SharedPreference
2. You can write the file on EXT sdcard by writeFileSaf as well as the other Saf fucntions.

[JNI Usage]

1. Use build.cmd to build libyurihook.so, then put libyurihook.so and libxhook.so to your app's lib
2. Load the libyurihook.so in your app
3. UsenativeInitSafJavaCallbacks() and nativeHookFile(String hooksoStr, String soPath)
   for jni file hook.
   hooksoStr, which passed to xhook_register, can use regex to match the hooked path(all of them are hooked), such as ".*\.so$"
   soPath, if not null, it will dlopen that path before hook