Add regression test for issue 91

Currently fails with:

    error: `"1_u32"` is not a valid identifier
      --> tests/test_expr.rs:56:49
       |
    56 |                         [<vec_ $bit>].insert(0, [<1_u $bit>]);
       |                                                 ^^^^^^^^^^^^
    ...
    63 |     vec_insert!(32);
       |     --------------- in this macro invocation
       |
       = note: this error originates in the macro `vec_insert` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0425]: cannot find function `vector_insert_32_bit` in this scope
      --> tests/test_expr.rs:64:5
       |
    64 |     vector_insert_32_bit(2);
       |     ^^^^^^^^^^^^^^^^^^^^ not found in this scope

tests/test_expr.rs

@@ -26,7 +26,7 @@ fn test_repeat() {
 }
 
 #[test]
-fn test_literals() {
+fn test_literal_to_identifier() {
     const CONST0: &str = "const0";
 
     let pasted = paste!([<CONST 0>]);
@@ -45,6 +45,25 @@ fn test_literals() {
     assert_eq!(pasted, CONST0);
 }
 
+#[test]
+fn test_literal_suffix() {
+    macro_rules! vec_insert {
+        ($bit:tt) => {
+            paste! {
+                fn [<vector_insert_ $bit _bit>](insert_size: usize) {
+                    let mut [<vec_ $bit>] = Vec::new();
+                    for _ in 0..insert_size {
+                        [<vec_ $bit>].insert(0, [<1_u $bit>]);
+                    }
+                }
+            }
+        };
+    }
+
+    vec_insert!(32);
+    vector_insert_32_bit(2);
+}
+
 #[test]
 fn test_underscore() {
     paste! {