[MLBEDSW-297] Setup and run on Microsoft Windows

Various updates to make vela run and produce identical output on
Microsoft Windows.
* Fixed overflow errors
* Fixed compile warnings
* Avoid problematic numpy version
* Updated README.md

Signed-off-by: Fredrik Svedberg <Fredrik.Svedberg@arm.com>
Change-Id: Ie48c63a92a00c81b3247d07f05b75d881319ddbb
diff --git a/ethosu/vela/softmax.py b/ethosu/vela/softmax.py
index 1bdab74..8b06129 100644
--- a/ethosu/vela/softmax.py
+++ b/ethosu/vela/softmax.py
@@ -520,7 +520,7 @@
                 [1, 1, 1, 512],
                 DataType.int32,
                 self.ONE_OVER_ONE_PLUS_X_LUT,
-                np.int32,
+                np.uint32,
                 TensorPurpose.LUT,
             )
         )