Reader flag to support unicode escapes in string literals

[avodonosov]

Despite the edn format doesn't specify unicode escapes in string literals (unlike for characters), in practice, it is very inconvenient sometimes. Optional support for unicode escapes in string literals, managed by reader config flag is very desirable.

See also: #65

[avodonosov]

Looking into the code I think unicode escapes are not even supported in characters. This is a bug - the EDN specification requires unicode escapes in characters: https://github.com/edn-format/edn#characters.

[avodonosov]

Mistakenly submitted this issue to a wrong repository. It was intended for https://github.com/bpsm/edn-java/