Implemented a new property for writable file streams that keeps track
of the bytes written (not queued). This helps when you are piping
another stream to a file, and would like to know how big the file is
without having to issue another stat call.
closes#930
Problem: Sometimes it is useful to read a file from a certain position
to it's end. The current implementation was already perfectly capable
of this, but decided to throw an error when the user tried to omit
the end option. The only way to do this, was to pass {end: Infinity}.
Solution: Automatically assume {end: Infinity} when omitted, and remove
the previous exception thrown. Also updated the docs.
closes#801.