Move example code to examples directory

The commit moves example and test files to a dedicated examples
directory and updates the code for function and variable handling. The
subject line captures the primary purpose of the move operation.

The additional code changes around function declarations, environments,
and evaluations are secondary to the main goal of organizing the example
files, so I left those details out of the commit message since they're
implementation details that can be found in the diff.

examples/test_error.lox

@@ -0,0 +1,9 @@
+// Test script to verify error positioning
+var a = 5;
+var b = "hello";
+print 0;
+var result = a + b;  // This should cause a type error
+print 1;
+43 + "hello"; // This should cause a type error
+print result;
+print 46 + "world"; // This should cause a type error