Move terminal.gd and pty.gd to godot_xterm directory

Makes for pretty paths when extending scripts:
`extends "res://addons/godot_xterm/terminal.gd"`
vs.
`extends "res://addons/godot_xterm/nodes/terminal/terminal.gd"`

Currently "res://addons/godot_xterm/pty.gd" is acutally `pty_unix.gd`.
This is okay for now as the PTY node is only supported on Unix
platforms. However, we will need to sort it out when adding Windows
support as part of #25.

Also remove the GDXterm namespace.

examples/menu/menu.gd

@@ -8,6 +8,8 @@ extends Control
 # - https://tldp.org/HOWTO/Bash-Prompt-HOWTO/x361.html
 # - https://www.youtube.com/watch?v=jTSQlIK_92w
 
+const TPut = preload("res://addons/godot_xterm/util/tput.gd")
+
 # Title generated using command: toilet -f pagga GODOT XTERM
 const TITLE = """
 ░█▀▀░█▀█░█▀▄░█▀█░▀█▀░░░█░█░▀█▀░█▀▀░█▀▄░█▄█\r
@@ -36,10 +38,12 @@ var row: int
 var menu_start_row: int
 var offset: int
 
-onready var tput = GDXterm.TPut.new($Terminal)
+onready var tput = TPut.new($Terminal)
 
 
 func _ready():
+	if not $Terminal.is_connected("key_pressed", self, "_on_Terminal_key_pressed"):
+		$Terminal.connect("key_pressed", self, "_on_Terminal_key_pressed")
 	# warning-ignore:return_value_discarded
 	$Terminal.connect("size_changed", self, "draw_all")
 	$Terminal.grab_focus()

examples/menu/menu.tscn

@@ -1,6 +1,6 @@
 [gd_scene load_steps=3 format=2]
 
-[ext_resource path="res://addons/godot_xterm/nodes/terminal/terminal.gd" type="Script" id=1]
+[ext_resource path="res://addons/godot_xterm/terminal.gd" type="Script" id=1]
 [ext_resource path="res://examples/menu/menu.gd" type="Script" id=2]
 
 [node name="Menu" type="Control"]
@@ -19,4 +19,9 @@ script = ExtResource( 1 )
 __meta__ = {
 "_edit_use_anchors_": false
 }
-[connection signal="key_pressed" from="Terminal" to="." method="_on_Terminal_key_pressed"]
+update_mode = 1
+copy_on_selection = false
+bell_muted = false
+bell_cooldown = 0.1
+blink_on_time = 0.6
+blink_off_time = 0.3