Add options.sourceType for disambiguating module parsing mode from script parsing mode

https://code.google.com/p/esprima/issues/detail?id=598
Remove the upper limit of hex digits in Unicode code point escapes

E.g. `'\u{00000000000000000001D306}' == '\u{1D306}'`.

https://code.google.com/p/esprima/issues/detail?id=612