libsemigroups/libsemigroups_pybind11: 0.6.0

This release contains a number of improvements and fixes, and adds support for the Konieczny class from libsemigroups. Add missing header include in cong.cpp by @james-d-mitchell in https://github.com/libsemigroups/libsemigroups_pybind11/pull/77 Remove trivial rules by @james-d-mitchell in https://github.com/libsemigroups/libsemigroups_pybind11/pull/79 Fix string encoding in KnuthBendix by @james-d-mitchell in https://github.com/libsemigroups/libsemigroups_pybind11/pull/82 Add support for Konieczny from libsemigroups by @james-d-mitchell in https://github.com/libsemigroups/libsemigroups_pybind11/pull/80 Better __repr__ for KnuthBendix by @james-d-mitchell in https://github.com/libsemigroups/libsemigroups_pybind11/pull/8