See release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.5.0.md
Please verify the PGP signatures of the releases before using. They are signed with belcher's pubkey (fingerprint: 0A8B 038F 5E10 CC27 89BF CFFF EF73 4EA6 77F3 1129, also found here, here and here)
The main body of changes in this release is to allow the codebase to run in both Python2 and Python3. The release notes describe how to choose which dependencies to use in the installation process.
Additionally there is a change to the backend libsecp256k1 binding (we now use coincurve which doesn't change any functionality (except removing an annoying compiler warning when running scripts!), see release notes for further details.
As there are a couple of bugfixes as detailed in the notes that fix potential crash conditions, Makers are strongly encouraged to update immediately.
Additional distribution note: Releases pre-0.4.2 have tags marked "unverified" now, because that gpg key expired; note that it has been signed with my new key (which I published widely, including on keyservers, some weeks ago), and that signature is in the /pubkeys directory. Also on the code-signing front, @undeath 's pubkey is now included in that same directory.