string_bytes: strip padding from base64 strings

Because of variations in different base64 implementation, it's been
decided to strip all padding from the end of a base64 string and
calculate its size from that.
timers: internal unref'd timer for api timeouts

When an internal api needs a timeout, they should use
timers._unrefActive since that won't hold the loop open. This solves
the problem where you might have unref'd the socket handle but the
timeout for the socket was still active.
net: use timers._unrefActive for internal timeouts