Added example contracts

Author: glarregay-tob

program-analysis/echidna/example/multiabi.sol

@@ -0,0 +1,32 @@
+pragma solidity ^0.8.0;
+
+contract Flag {
+
+   bool flag = false;
+
+   function flip() public {
+       flag = !flag;
+   }
+
+   function get() public returns (bool) {
+        return flag;
+   }
+
+   function test_fail() public {
+       assert(false);
+   }
+}
+
+
+contract EchidnaTest {
+   Flag f;
+
+   constructor() {
+      f = new Flag();
+   }
+
+   function test_flag_is_false() public {
+      assert(f.get() == false);
+   }
+
+}

program-analysis/echidna/example/multiabi.yaml

@@ -0,0 +1,3 @@
+testMode: assertion
+testLimit: 50000
+multi-abi: true