Allow skipping to the end of a message without reading all the groups and var data

[mjpt777]

Add a method something like Decoder.skipToEnd().

[tamboril]

I agree. I've had to roll my own for scanning to a specific group as quickly as possible, and it's not easy due to the stateful nature of the parser and the private state variables, such as index.

[adkapur]

Oh nice this is the impetus for --> FIXTradingCommunity/fix-simple-binary-encoding#53

[mjpt777]

Fixed with #865