Add configurable recursion limit to the decoder

Doesn't appear to have a measurable performance impact on the
benchmarks.
Perl: Version bump changelog for decoder
Add Sereal logo
add diagnostics and asserts temporarily
fix hash weakrefs maybe/hopefully (no tests yet)
simplify condition
Add configurable recursion limit to the Encoder
Changelog for previous commit
Perl: Version bump and changelog
Capitalize Booking.com
Fix repository location
Perl: "Sereal" meta distribution

The "Sereal" module/distribution depends on both encoder and decoder for
convenience. It will always depend on the most recent version of both
that have a lower or equal version as the Sereal meta-distribution
itself.

This is not Task::Sereal since it actually offers Sereal encoder and
decoder functions for exporting. (Tasks are just dependency vehicles.)
Properly versioned dependencies on encoder&decoder
version bump, changelog
Perl decoder: Configurable limit on number of hash entries

This is to be able to respond to future hash collision attacks easily.
Tests for hash-entry count limit
Perl, encoder: Version bump, copyright update
Perl, decoder: Version bump, changelog for release
Perl, decoder: Minor test warning fix
Perl: Reflect new decoder release in meta dist