Stack component implemented (more flex than stack)

ROADMAP.md

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+* stack component
+
+* negative absolution position (from right/bottom)
+
+* flex component
+
+* layout (constraint)
+
+* scroll
+
+* button
+
+* projected vertex/raw vertex mode (projection on GPU)
+
+* VAO/VBO in windows (batched)
+
+* pool/wait mode mechanism
+
+* better font rendering : signed distance
+
+* Rich text component : parsing html? making list of struct of texts (with style information for the rendering)