Support "current position" (position=null) writes, reads

[innerop]

Hi

Awesome that you made this.

I’d like to do a benchmark based on your work for fileAppend and wondering if I can supply nulls for offset in position in writeBuffer so it just appends the data at end of file.

Is that supported?

If not, I can take a stab at it, although my knowledge of C++ is very rusty.

Thanks for sharing!