feat: support memoize package (closes #16)

Inject `\mmzUnmemoizable` into progress bar tikzpictures to avoid the
memoize package memoizing them. Also provide a dummy for this command in
case the memoize package is not loaded.

src/beamerinnerthememoloch.dtx

@@ -202,6 +202,7 @@
 \setbeamertemplate{title separator}{
   \tikzexternaldisable%
   \begin{tikzpicture}
+    \mmzUnmemoizable%
     \fill[fg] (0,0) rectangle (\textwidth, \moloch@titleseparator@linewidth);
   \end{tikzpicture}%
   \tikzexternalenable%
@@ -342,6 +343,7 @@
   }
   \tikzexternaldisable
   \begin{tikzpicture}
+    \mmzUnmemoizable%
     \fill[bg]
     (0,0)
     rectangle

src/beamerouterthememoloch.dtx

@@ -199,6 +199,7 @@
   \begin{beamercolorbox}[wd=\paperwidth]{progress bar in head/foot}
     \tikzexternaldisable
     \begin{tikzpicture}
+      \mmzUnmemoizable%
       \fill[bg]
       (0,0)
       rectangle

src/beamerthememoloch.dtx

@@ -56,10 +56,13 @@
 % them with ``tikzexternalenable'' and ``tikzexternaldisable''. However, if the
 % ``external'' libray is not loaded we would get undefined control sequence
 % problems, hence we define them as no-ops if they are not defined yet.
+% We do the same for the \mmzUnmemoizable command from the memoize package, in
+% order to avoid memoization of the progress bars.
 %
 %    \begin{macrocode}
 \providecommand{\tikzexternalenable}{}
 \providecommand{\tikzexternaldisable}{}
+\providecommand{\mmzUnmemoizable}{}
 %    \end{macrocode}
 %
 % \subsubsection{Component sub-packages}