Implement view buffer lifetime extension for remote_cx::as_rpc

[Dan Bonachea]

As noted in pull request #110 and spec issue #147, we don't currently implement the specified view buffer lifetime extension for RPCs injected using remote_cx::as_rpc

I'm about to add this to the known compliance violation list, but @john bachan will consider fixing it next week in time for the code freeze.

[Dan Bonachea]

Bulk roll-over of unresolved issues to next milestone

[Dan Bonachea]

Bulk roll-over of unresolved issues to next milestone

[Amir Kamil]

Resolved by PR #263.