Set read timeout separately from connect timeout

[FGasper]

Would it be feasible to introduce either of two changes:

1. A read_timeout setting that defaults to the regular timeout but is used as an override when HTTP::Tiny::Handle is instantiated

2. The ability to specify a class to use in place of HTTP::Tiny::Handle (which would allow implementors to subclass H::T::Handle to achieve a custom tiemout)

Right now the same timeout length is always used for the connect as for reads, though H::T::Handle accepts its own timeout and thus could accommodate a distinct value.