Support for trybuild and similar macro testing tools (#168)

Signed-off-by: Filippo Costa <filippo@neysofu.me>

tests/tests/trybuild.rs

@@ -0,0 +1,6 @@
+#[test]
+fn test_trybuild() {
+    let t = trybuild::TestCases::new();
+    t.pass("tests/trybuild/empty_main.rs");
+    t.compile_fail("tests/trybuild/fail_to_compile.rs");
+}

tests/tests/trybuild/empty_main.rs

@@ -0,0 +1 @@
+fn main() {}

tests/tests/trybuild/fail_to_compile.rs

@@ -0,0 +1,3 @@
+fn main() {
+    "foobar".foobar();
+}

tests/tests/trybuild/fail_to_compile.stderr

@@ -0,0 +1,5 @@
+error[E0599]: no method named `foobar` found for reference `&'static str` in the current scope
+ --> tests/trybuild/fail_to_compile.rs:2:14
+  |
+2 |     "foobar".foobar();
+  |              ^^^^^^ method not found in `&str`