CDRIVER-4173 clarify the `reply` contains the full server reply (#1263)

* note that `reply` contains full server reply

* fix documented return of `mongoc_collection_find_and_modify`

* remove notes of MongoDB 3.2

The minimum supported server version of the C driver is 3.6. Documentation can assume user is using 3.6 or newer.

* link to findAndModify command manual page

* group "returns `false`" and "sets `error`"

Co-authored-by: vector-of-bool <vectorofbool@gmail.com>

* Revert "remove notes of MongoDB 3.2"

This reverts commit 591ade57d4bd2f78c8d98d9e3e7729ae153f9ea2.

* add replacement for findAndModify

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Co-authored-by: vector-of-bool <vectorofbool@gmail.com>