Added new opcode OP_ENV to provide an env() function to get environment variables from your OS.

examples/os_env.fun

@@ -0,0 +1,18 @@
+#!/usr/bin/env fun
+
+// Environment variables via env(name):
+// - Returns the value as a string.
+// - If the variable is not set, returns an empty string.
+
+print("HOME=" + env("HOME"))
+print("SHELL=" + env("SHELL"))
+print("FUN_NOT_SET=" + env("FUN_NOT_SET"))
+
+// You can use it in scripts, e.g.:
+fun greet()
+  user = env("USER")
+  if user == ""
+    print("Hello, mysterious friend!")
+  else
+    print("Hello, " + user + "!")
+greet()