Improve latex output.

Former-commit-id: 0a695725a07ee72373d0d96b246ee503e1e88263

src/Reanimate/Examples.hs

@@ -332,6 +332,6 @@ latex_basic = proc () -> do
   duration 1 -< ()
   emit -< do
     rect_ [width_ "100%", height_ "100%", fill_ "black"]
-    g_ [transform_ $ translate 5 50] $
+    g_ [transform_ $ translate 20 20] $
       g_ [transform_ $ scale 4 4, fill_ "white"] $
-        latex "$\\sum_{k=1}^\\infty {1 \\over k^2} = {\\pi^2 \\over 6}$"
+        latex "\\sum_{k=1}^\\infty {1 \\over k^2} = {\\pi^2 \\over 6}"

src/Reanimate/LaTeX.hs

@@ -93,6 +93,10 @@ tex_prologue =
   \\\DisableLigatures{encoding = *, family = * }\n\
   \%\\usepackage[UTF8]{ctex}\n\
   \\\linespread{1}\n\
-  \\\begin{document}\n"
+  \\\begin{document}\n\
+  \\\begin{align*}\n"
 
-tex_epilogue = "\n\\end{document}"
+tex_epilogue =
+  "\n\
+  \\\end{align*}\n\
+  \\\end{document}"