[collections] Add a convenience module.

This module ('collections') re-exports set, bit-set, bit-vector and
byte-vector.
Release note for collections convenience module.
Merge pull request #397 from abeaumont/documentation-join

[doc] Documentation fixes in join generic function and method pointed by @cgay
Typo fix.
Prefer OPEN_DYLAN_USER_REGISTRIES over ./registry
Merge pull request #400 from cgay/user-registry-path

Prefer OPEN_DYLAN_USER_REGISTRIES over ./registry
Merge pull request #391 from waywardmonkeys/collections-module

[collections] Add a convenience module.
Fix typos.
Categorize release changes in improvements and bugfixes