Allow multiline query strings

Although Gemini does not imply this, posting small multiline text to server can be of great use.
Some clients (Lagrange) do already support this.

av98.py

@@ -274,7 +274,8 @@ class GeminiClient(cmd.Cmd):
             "auto_follow_redirects" : True,
             "gopher_proxy" : None,
             "tls_mode" : "tofu",
-            "cache" : False
+            "cache" : False,
+            "editor": None
         }
 
         self.log = {
@@ -445,6 +446,20 @@ you'll be able to transparently follow links to Gopherspace!""")
                 user_input = getpass.getpass("> ")
             else:
                 user_input = input("> ")
+                if user_input == "":  # Empty input switches to multiline editor
+                    try:
+                        multiline_comment =\
+                            "\n# One line is not enough for your input?" +\
+                            "\n# Then please type & save the whole query, leaving this comment untouched."
+                        with tempfile.NamedTemporaryFile(suffix=".tmp", delete=False) as tfc:
+                            tfc.write(multiline_comment.encode("utf-8"))
+                        subprocess.call([self.options.get("editor", os.environ.get("EDITOR", "vim")), tfc.name])
+                        with open(tfc.name, "r", encoding="utf-8") as tfr:
+                            user_input = tfr.read().strip()
+                            if user_input.endswith(multiline_comment):
+                                user_input = user_input[:-len(multiline_comment)]
+                    finally:
+                        os.unlink(tfc.name)
             return self._fetch_over_network(gi.query(user_input))
 
         # Redirects