Fix line numbers being wrong with macro expansion

Addresses https://github.com/icy-arctic-fox/spectator/issues/18

spec/line_number_spec.cr

@@ -0,0 +1,27 @@
+require "./spec_helper"
+
+Spectator.describe Spectator do
+  let(current_example) { ::Spectator::Harness.current.example }
+  subject(source) { current_example.source }
+
+  context "line numbers" do
+    subject { source.line }
+
+    it "match source code" do
+      is_expected.to eq(__LINE__ - 1)
+    end
+
+    it "handles multiple lines and examples" do
+      # Offset is important.
+      is_expected.to eq(__LINE__ - 2)
+    end
+  end
+
+  context "file names" do
+    subject { source.file }
+
+    it "match source code" do
+      is_expected.to eq(__FILE__)
+    end
+  end
+end