Add some shortcodes for making the game theory post nicer.

assets/scss/gametheory.scss

@@ -0,0 +1,11 @@
+@import "variables.scss";
+@import "mixins.scss";
+
+.assumption-number {
+    font-weight: bold;
+}
+
+.assumption {
+    @include bordered-block;
+    padding: 0.8rem;
+}