Added two more examples

examples/leader_election.pnet

+petri net "leader election 2" {
+    places {
+        s1 s1x1 s1x2
+        s2 s2x1 s2x2
+        lead
+    }
+    transitions {
+        s1send1 s1pass2    s1accept1
+        s2send2 s2discard1 s2accept2
+        newleader
+    }
+    arcs {
+        s1   -> s1send1    -> s1x1
+        s2   -> s2send2    -> s2x2
+        s1x1 -> s2discard1
+        s1x2 -> s2accept2  -> lead
+        s2x1 -> s1accept1  -> lead
+        s2x2 -> s1pass2    -> s1x2
+        lead -> newleader  -> { s1 s2 }
+    }
+    initial { s1 s2 }
+}
+safety property {
+    lead >= 2
+}
+liveness property {
+    newleader > 0 || newleader = 0
+}

examples/snapshot.pnet

+petri net "snapshot 2" {
+    places {
+        white1 red1 received1 notreceived1 sent1 notsent1 marker1 sample1 done1
+        white2 red2 received2 notreceived2 sent2 notsent2 marker2 sample2 done2
+    }
+    transitions {
+        init1 receive_white1 receive_red1 send1
+        init2 receive_white2 receive_red2 send2
+        snapshot
+        reset1
+        reset2
+    }
+    arcs {
+        white1 -> init1 -> { red1, sample1 }
+        { white1, notreceived1, marker2 } -> receive_white1 -> { red1, received1, sample1 }
+        { red1, notreceived1, marker2 } -> receive_red1 -> { red1, received1 }
+        { red1, notsent1 } -> send1   -> { red1, sent1, marker1 }
+
+        white2 -> init2 -> { red2, sample2 }
+        { white2, notreceived2, marker1 } -> receive_white2 -> { red2, received2, sample2 }
+        { red2, notreceived2, marker1 } -> receive_red2 -> { red2, received2 }
+        { red2, notsent2 } -> send2   -> { red2, sent2, marker2 }
+
+        { sample1, sample2 } -> snapshot -> { done1, done2 }
+
+        { red1, done1, received1, sent1 } -> reset1 -> { white1, notreceived1, notsent1 }
+        { red2, done2, received2, sent2 } -> reset2 -> { white2, notreceived2, notsent2 }
+    }
+    initial {
+        white1 notreceived1 notsent1
+        white2 notreceived2 notsent2
+    }
+}
+liveness property {
+    init2 = 0
+}