take \tikzpicture out of karnaugh-map environment

This allows the user to place their own tikzpicture environment around
the karnaugh-map-inner environment, which makes the package compatible
with tikz externalization.

Author: myzhang1029

karnaugh-map.dtx

@@ -329,6 +329,17 @@
 % ^^A ##########################################################################
 % ^^A ##########################################################################
 \NewDocumentEnvironment{karnaugh-map}{D(){} s O{4} O{4} O{1}} {%
+  \begin{tikzpicture}
+  \IfBooleanTF{#2}{%
+    \begin{karnaugh-map-inner}(#1)*[#3][#4][#5]%
+  }{%
+    \begin{karnaugh-map-inner}(#1)[#3][#4][#5]%
+  }
+}{%
+  \end{karnaugh-map-inner}
+  \end{tikzpicture}
+}
+\NewDocumentEnvironment{karnaugh-map-inner}{D(){} s O{4} O{4} O{1}} {%
   \begingroup
     % parse environment options
     \setkeys{karnaugh-map}{#1}%
@@ -366,7 +377,6 @@
     % to parse remaining arguments and finish initialization.
     \@karnaughmap@func@karnaughstart@%
 }{
-    \end{tikzpicture}
   \endgroup
 }
 \DeclareDocumentCommand{\@karnaughmap@func@karnaughstart@}{oooooo} {%
@@ -564,14 +574,14 @@
       Existing templates have the following dimensions: 2x2x1, 2x4x1, 4x2x1, 4x4x1, 4x4x2, and 4x4x4.
     }%
   \fi
-  \begin{tikzpicture}[
+  \tikzset{
     LineStyleA/.style={semithick,solid},
     LineStyleB/.style={semithick,dash dot dot},
     LineStyleC/.style={thin,double distance=0.8pt},
     LineStyleD/.style={ultra thick},
     LineStyleE/.style={semithick,dashed},
     LineStyleF/.style={semithick,densely dotted},
-  ]
+  }
     % grid {[START]
       % for all dimensions
       \draw[color=black, ultra thin] (0,0) grid (\@karnaughmap@var@mapsizex@,\@karnaughmap@var@mapsizey@);