Fix string literal support

[uunnii]

1. Unquote string
2. Using Golang string syntax

name = "ab\"c" // ab"c

name = "ab\u2333c" // ab⌳c

name = "ab\\u2333c" // ab\u2333c

name = "Hello, 世界" // Hello, 世界

name = "Hello, \u4e16\u754c" // Hello, 世界

name = "ab
c" // syntax error