Add tests.

test/shebang/shebang.wren

@@ -0,0 +1,2 @@
+#!/bin/wren
+IO.print("ok") // expect: ok

test/shebang/shebang_at_eof.wren

@@ -0,0 +1 @@
+#!/bin/wren

test/shebang/shebang_at_other_line.wren

@@ -0,0 +1,3 @@
+// expect error line 3
+IO.print("nope")
+#!/bin/wren