jdavidberger authored Jul 27, 2017 and Brad King committed Nov 29, 2017

The `uv_*_t` handle types are closed by `uv_close`, but the semantics
are tricky.  Calling `uv_close` may not close immediately.  Instead it
hands ownership to the uv loop to which the handle is currently
attached.  When the loop decides to close it, a callback is used to
allow the `uv_close` caller to free resources.

Provide an abstraction layer as `cm::uv_*_ptr` types corresponding to
the `uv_*_t` handle types.  Each pointer is either empty (`nullptr`)
or has an initialized handle attached to a loop.  Use move semantics
to ensure a single owner of the handle so that clients can predict
when the handle is destroyed.