Add functions, while loops, and vars support (#264)

* Add functions, while loops, and vars support

* Add back REPEAT

* Add support for nested WHILE loops in function

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Co-authored-by: Tony Le <tonyle@coxautoinc.com>

examples/functions.dd

@@ -0,0 +1,13 @@
+REM Example Function
+FUNCTION COUNTDOWN()
+	REM The next four lines open Notepad in Windows and type "Hello World!"
+	GUI r
+	DELAY 1000
+	STRING notepad
+	ENTER
+	DELAY 2000
+	STRING Hello World!
+	ENTER
+END_FUNCTION
+COUNTDOWN()
+

examples/while_loops.dd

@@ -0,0 +1,7 @@
+VAR $TIME = 3
+WHILE ($TIME > 0)
+	STRING .
+	DELAY 500
+	STRING While Looop!!
+	ENTER
+END_WHILE