Slightly shorten braces for marking structs in memorystack.

When two structs are shown in top of each other in the stacks, the
braces touch. By shortening them by 2pt, there is a visual separation
now.

talk/setup.tex

@@ -401,7 +401,7 @@
   \memorystackset{
     size y/.get=\stacksizey
   }
-  \draw[snake=brace,thick] (-2pt,#1*\stacksizey-\stacksizey) -- (-2pt,#2*\stacksizey)
+  \draw[snake=brace,thick] (-2pt,#1*\stacksizey-\stacksizey+2pt) -- (-2pt,#2*\stacksizey-2pt)
     node [midway, above, sloped] {#3};
 }