Make current token kind public and accessible via Lexer.CurrentToken

[stiletto]

Currently it's there is no way to decode dynamically typed JSON other than Lexer.Interface().

Sometimes you want to implement some kind of dynamic typing, for example accepting strings and bools, or strings and numbers and want to parse differently depending on the token kind.
Lexer.Interface makes it possible but is too powerful for simple use-cases and doesn't allow you to limit expected types to protect from malicious input - it would happily decode nested maps of nested maps.

This pull request makes tokenKind public and allows the kind of current token to be accessed via Lexer.CurrentToken()

[GoWebProd]

Thanks for the PR. Since the PR is old and perhaps it is irrelevant for you, I will close it. If it is relevant, open it again, resolve conflicts and I will gladly merg4e.