Add a file picker to pick files from $HOME

This allows e.g. files from the $HOME folder to be attached to emails
or uploaded when in other apps.

Also bump version to 0.18.

app/src/main/java/com/termux/filepicker/TermuxFilePickerProvider.java

@@ -0,0 +1,50 @@
+package com.termux.filepicker;
+
+
+import android.content.ContentProvider;
+import android.content.ContentValues;
+import android.database.Cursor;
+import android.net.Uri;
+import android.os.ParcelFileDescriptor;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+
+/** Provider of files content uris picked from {@link com.termux.filepicker.TermuxFilePickerActivity}. */
+public class TermuxFilePickerProvider extends ContentProvider {
+    @Override
+    public boolean onCreate() {
+        return false;
+    }
+
+    @Override
+    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
+        return null;
+    }
+
+    @Override
+    public String getType(Uri uri) {
+        return null;
+    }
+
+    @Override
+    public Uri insert(Uri uri, ContentValues values) {
+        return null;
+    }
+
+    @Override
+    public int delete(Uri uri, String selection, String[] selectionArgs) {
+        return 0;
+    }
+
+    @Override
+    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
+        return 0;
+    }
+
+    @Override
+    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
+        File file = new File(uri.getPath());
+        return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
+    }
+}