Added directfs

Added a very rudimentary file I/O system suitable for experimenting
with the language further. A better one will be designed when we have
sensible error management.

examples/file-browser/main.orc

@@ -0,0 +1,31 @@
+import system::(io, directfs, async)
+import std::proc::*
+import std::(to_string, to_uint)
+
+const folder_view := \path.\next. do{
+  cps println $ "Contents of " ++ path;
+  cps entries = async::block_on $ directfs::readdir path;
+  cps list::enumerate entries
+    |> list::map (pass \id. pass \name.\is_dir. (
+      println $ to_string id ++ ": " ++ name ++ if is_dir then "/" else ""
+    ))
+    |> list::chain;
+  cps print "select an entry, or .. to move up: ";
+  cps choice = readln;
+  let output = if choice == "..\n"
+    then directfs::pop_path path
+      |> option::unwrap
+      |> tuple::pick 0 2
+    else (
+      to_uint choice
+        |> (list::get entries)
+        |> option::unwrap
+        |> (directfs::join_paths path)
+    );
+  next output
+}
+
+const main := loop_over (path = "/home/lbfalvy/Code/orchid/examples") {
+  cps path = folder_view path;
+}
+