v4.0.1 of libmusicbrainz4 has now been released. This is primarily a maintenance release to fix a couple of bugs that were reported. Additionally, the code has now moved to GitHub, and can now be found at
https://github.com/metabrainz/libmusicbrainz.
The main changes are:
- Fixed bug LMB-30 – Unable to access all relation lists on objects with multiple relation lists
- Fixed bug LMB-31 – mb_relationlist_get_targettype always returns “target-type”
The interface has changed as regards to retrieving relation lists, due to LMB-30. Previously, the library only returned the last relation list that was returned in the XML response. The old ‘RelationList’ method on the Artist, Label, Recording, Release, ReleaseGroup and Work classes has been marked ‘deprecated’, and a new ‘RelationListList’ method will return a list of all relation lists for the entity.
For backwards compatibility, the ‘RelationList’ method will operate in the same manner as release 4.0.0, only returning the last relation list.
As ever, please see the enclosed README for details on support and bug reporting. The release is available for download at http://musicbrainz.org/doc/libmusicbrainz.
MetaBrainz Blog 
The link to github is wrong, https://github.com/metabrainz/libmusicbrainz
Yes, there was a reorganisation of the GIT repositories on GitHub to make things more consistent.
The next version is due soon, and the announcement will contain the correct URLs.
I’ll see if someone can edit this post to update it.
Andy