Bug: Divert target variable declaration order

First of all, let me just say that I have been using Ink for the past couple of days and it is beyond amazing. Thank you so much for sharing this great project with the community.

I recently ran into what I believe is a bug with divert target variables.

```
=== top_knot ===
Herein, I test divert targets.
-> _MyDivertTarget

=== diversion ===
What a nice diversion!
->END

VAR _MyDivertTarget = -> diversion
```

This code fails to compile, with the error message "Divert target not found: '-> _MyDivertTarget.' By messing around with the this, I was able to get the following to compile:

```
-> top_knot

VAR _MyDivertTarget = -> diversion

=== top_knot ===
Herein, I test divert targets.
-> _MyDivertTarget

=== diversion ===
What a nice diversion!
->END
```

I don't believe this is the expected behavior, since I've found that otherwise, the order of varaible declaration doesn't matter. Along the same lines, if I print the value of _MyDivertTarget in the first example without trying to divert to it, it says "debug DivertTargetValue(diversion)" - so it recognizes the variable in one context, but as soon as I try to actually divert to it, the compiler throws an error.