Add End Keyword

End-Keyword.md

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+Keyword: `end`
+
+Syntax: `end $int`
+
+Time Complexity: 
+
+## Overview
+The `end` keyword exits the program, returning an error status code to the OS. The argument is the status code returned.
+
+## Example usage
+To cleanly end a program, add `end 0` to the end of a script. (0 means the program successfully completed with no errors).
+```grnd
+# main code
+end 0
+```
+
+If there was some sort of error, use a different exit status code.
+```grnd
+if $wasError %error # if there was an error, jump to @error
+end 0 # if it didn't jump (i.e. no error), exit with status code 0
+@error
+end 1 # if there was an error, exit with status code 1
+```