Provide `from_slice_lax` methods about etherparse

[robs-zeynet]

FYI: I just pulled master as part of my pull request and tried to run it and it broke most of my project :-( A super common case for "lax" parsing is an ICMP TTL Unreachable message which has a fraction of the expired packet as the ICMP message's payload. The 'fraction' is defined as the full IP header and "at least 8 bytes" of the transport header, which depending on the router may be exactly 8 bytes or maybe the full packet plus an ICMP Extension.

Is the plan for this "from_slice_lax" to end up in 0.14 before it ships? Can I help? Thanks in advance.

[JulianSchmid]

@robs-zeynet The plan is to ship the next version with a lax parser, otherwise I kind of pull support for something I supported previously.

That is actually the main reason why I have not yet released a new version, even though quiet a lot of changes have pilled up on the master branch. But I wanted to be done waaay earlier, but life happened and I did not find enough time the last few months.

[JulianSchmid]

Implemented in https://github.com/JulianSchmid/etherparse/releases/tag/v0.14.0