Disambiguate "" empty strings from multiline strings properly.

Previously `""` would go into multiline mode and thus *require* a
following ".

src/parser.rs

@@ -265,11 +265,16 @@ impl<'a> Parser<'a> {
         let mut multiline = false;
         let mut ret = String::new();
 
-        // detect multiline literals
+        // detect multiline literals, but be careful about empty ""
+        // strings
         if self.eat('"') {
-            multiline = true;
+            if self.eat('"') {
-            if !self.expect('"') { return None }
+                multiline = true;
-            self.eat('\n');
+                self.eat('\n');
+            } else {
+                // empty
+                return Some(String(ret))
+            }
         }
 
         loop {

src/test/valid.rs

@@ -122,6 +122,9 @@ test!(long_float,
 test!(long_integer,
        include_str!("valid/long-integer.toml"),
        include_str!("valid/long-integer.json"))
+test!(string_empty,
+       include_str!("valid/string-empty.toml"),
+       include_str!("valid/string-empty.json"))
 test!(string_escapes,
        include_str!("valid/string-escapes.toml"),
        include_str!("valid/string-escapes.json"))

src/test/valid/string-empty.json

@@ -0,0 +1,6 @@
+{
+    "answer": {
+        "type": "string",
+        "value": ""
+    }
+}

src/test/valid/string-empty.toml

@@ -0,0 +1 @@
+answer = ""