stream: Implement slice:// for reading slices of streams

Add support for reading a byte range from a stream via
 the `slice://` protocol.

 Syntax is `slice://start[-end]@URL` where end is a maximum
 (read until end or eof).

 Size suffixes support in `m_option` is reused so they can
 be used with start/end.

 This can be very useful with e.g. large MPEGTS streams with
 corruption or time-stamp jumps or other issues in them.

Signed-off-by: Mohammad AlSaleh <CE.Mohammad.AlSaleh@gmail.com>