migrate langref documentation generation to the build system

doc/langref/test_misaligned_pointer.zig

@@ -0,0 +1,24 @@
+const std = @import("std");
+const expect = std.testing.expect;
+
+const BitField = packed struct {
+    a: u3,
+    b: u3,
+    c: u2,
+};
+
+var bit_field = BitField{
+    .a = 1,
+    .b = 2,
+    .c = 3,
+};
+
+test "pointer to non-byte-aligned field" {
+    try expect(bar(&bit_field.b) == 2);
+}
+
+fn bar(x: *const u3) u3 {
+    return x.*;
+}
+
+// test_error=expected type