Fix multi-line strings are not allowed for key

In spec https://github.com/toml-lang/toml#keys

Quoted keys are clarified as

> he exact same rules as either basic strings or literal strings

TOML clearly distinguishes basic string and multi-line basic string
(literal string is also).

https://github.com/toml-lang/toml#string

So table key and quoted key should not allow multi-line basic string
and multi-line literal string.

ABNF definition also describes that.

https://github.com/toml-lang/toml/blob/master/toml.abnf

```
string = ml-basic-string / basic-string / ml-literal-string / literal-string

quoted-key = basic-string / literal-string
```

`string` contains `ml-*` but `quoted-key` doesn't.

1 files changed, 6 insertions, 0 deletions

diff --git a/test-suite/tests/parser.rs b/test-suite/tests/parser.rs
index 2282416..2534ce6 100644
--- a/test-suite/tests/parser.rs
+++ b/test-suite/tests/parser.rs
@@ -275,6 +275,10 @@ fn bad_keys() {
     "\"\"|=3".parse::<Value>().unwrap_err();
     "\"\n\"|=3".parse::<Value>().unwrap_err();
     "\"\r\"|=3".parse::<Value>().unwrap_err();
+    "''''''=3".parse::<Value>().unwrap_err();
+    "\"\"\"\"\"\"=3".parse::<Value>().unwrap_err();
+    "'''key'''=3".parse::<Value>().unwrap_err();
+    "\"\"\"key\"\"\"=3".parse::<Value>().unwrap_err();
 }
 
 #[test]
@@ -290,6 +294,8 @@ fn bad_table_names() {
     "[']".parse::<Value>().unwrap_err();
     "[''']".parse::<Value>().unwrap_err();
     "['''''']".parse::<Value>().unwrap_err();
+    "['''foo''']".parse::<Value>().unwrap_err();
+    "[\"\"\"bar\"\"\"]".parse::<Value>().unwrap_err();
     "['\n']".parse::<Value>().unwrap_err();
     "['\r\n']".parse::<Value>().unwrap_err();
 }