adding skip parameters to stream_in function

[jadaliha]

Following the stack overflow question:
https://stackoverflow.com/questions/53269796/import-ndjson-into-r-skip-first-n-lines/53270571?noredirect=1#comment93457405_53270571

I feel it is very useful to have skip parameters in stream_in function. It let us to skip first n lines of stream. plus we could use this to read big Files in chunck.