Add lambda tests

valid/function/lambdas/callLambdaInALoop.wacc

+# Call lambdas repetitively 
+
+# Output:
+# 0
+# 1
+# 2
+# 3
+# 4
+
+# Program:
+
+begin
+    int n = 5
+    int i = 0 ;
+    while i < n do
+      println call (\() -> i)() ;
+      i = i + 1;
+    done ;
+end

valid/function/lambdas/callSimpleLambda.wacc

+# Assign to a variable ad print the result of the lambda
+
+# Output:
+# 6
+
+# Program:
+begin
+  int y = call (\(int x, int y) -> x * y)(2, 3);
+  print y
+end
\ No newline at end of file

valid/function/lambdas/lambdaInsideFunction.wacc

+# Call lambda inside a function
+
+# Output:
+# 6
+
+# Program:
+begin
+  int f(int x, int y) is
+    return call (\(int x, int y) -> x * y)(x,y)
+  end
+  int y = f(2,3)
+  print y
+end
\ No newline at end of file

valid/function/lambdas/lambdaWithManyArgs.wacc

+# call lambdas repetitively 
+
+# Output:
+# 5
+
+# Program:
+
+begin
+    print call (\(int x, int y, bool z, bool a, bool b, string c) -> x + y)(2, 3, false, false, true, "hello")
+end
\ No newline at end of file

valid/function/lambdas/simpleLambda.wacc

+# a simple lambda is declared, but not called
+
+# Output:
+# #empty#
+
+# Program:
+
+begin
+    call (\(int x, int y) -> x * y)(2, 3)
+    skip
+end