Make packed fs always available, and manually settable

src/fs.h

@@ -44,7 +44,28 @@ struct mg_str mg_file_read(struct mg_fs *fs, const char *path);
 bool mg_file_write(struct mg_fs *fs, const char *path, const void *, size_t);
 bool mg_file_printf(struct mg_fs *fs, const char *path, const char *fmt, ...);
 
-// Packed API
-const char *mg_unpack(const char *path, size_t *size, time_t *mtime);
-const char *mg_unlist(size_t no);             // Get no'th packed filename
+
+// A piece of memory (flash or RAM) represented as a file
+struct mg_mem_file {
+  const char *path;
+  const unsigned char *data;
+  size_t size;   // Data size
+  time_t mtime;  // Modification time
+};
+
+// Global variable that points to the array of memory files. It can be
+// changed to point to the user-defined file array. The last element
+// should have NULL path.
+//
+// static const struct mg_mem_file my_files[] = {
+//   {"/web_root/index.html", "hi", 2, 0},
+//   {NULL, NULL, 0, 0},
+// };
+// mg_mem_files = my_files;
+extern const struct mg_mem_file *mg_mem_files;
+
+// const char *mg_unpack(const char *path, size_t *size, time_t *mtime);
+// const char *mg_unlist(size_t no);             // Get no'th packed filename
 struct mg_str mg_unpacked(const char *path);  // Packed file as mg_str
+
+extern const struct mg_mem_file mg_packed_files[];  // Generated by "pack" util