New features

Added per-sender-IP connection limiting to reduce the risk of non-distributed DoS against letmeind. See options --num-connections and the new option --num-ip-connections.
The client code (crate letmein) has been converted into a library+binary crate to allow integration of client functionality into arbitrary applications.

Incompatible changes

The jump rule chain names have been limited to 64 characters to ensure the kernel name length is always honored. If your chain names are longer than 64 characters, please shorten them.
Chain names have been restricted to the character set: [a-zA-Z0-9_-.] If your chain names use other characters, please convert to this character set.
Some sanity checks have been added to the configuration file parser. It will now abort on things like duplicate section names and duplicate option names. Such configurations were never considered to be valid and the actual outcome was confusing. Therefore, they are now disallowed.

These incompatible changes have been made to harden the system against possible misconfiguration and possible resulting security problems.

The cryptography crates have been updated to new versions and new modern alternatives.