Use regexp to replace the escaping characters,but not decode function

I see the code [#L58](https://github.com/marksteve/toml-ply/blob/master/toml_ply.py#L58):

```
t.value = t.value[1:-1].decode('string-escape')
```
This got unicode strings crashed.

But the regexp way ok:

```
>>> from toml_ply import loads
>>> loads(u'a = "你好"')
{u'a': u'\u4f60\u597d'}

```

Using regexp to process the escaping chars seems to be the right approach.