Add readSome / writeSome methods

Issue #153 wontfix
Kaya Kupferschmidt
created an issue

Sockets (and some other stream types) should have readSome/writeSome methods which are allowed to process only part of a buffer. The read/write methods should always try to write the whole buffer. Maybe readSome/writeSome only makes sense in async I/O anyway.

Maybe some additional interface would be appropriate or we simply implement this in the abstract class AbstractInputStream / AbstractOutputStream.

HttpInputStream and HttpOutputStream then could be simplified at some places.