Add a guide example for rput(remote_cx::as_rpc())

[Dan Bonachea]

rput(remote_cx::as_rpc()) is an important tool for UPC++ programming, especially when replacing code written for a message-passing model that requires/expects coupling of data transfer with synchronization.

Unfortunately our current training content for this technique is lacking.

We should write a guide section and example (probably a new subsection of Ch10) to cover this topic.

[Dan Bonachea]

Mass roll-over of open issues to next release milestone

[Dan Bonachea]

Work in PG PR 23

[Dan Bonachea]

Merge PG PR 23 merged at 51313d7