5.3.0

This release contains a fairly large number of changes, fixes, and improvements. The biggest changes/new features in this release are:

• The build system has been completely updated by @fingolfin and @dimapase:
  • Convert buildsystem to use Makefile.gappkg instead of automake by @fingolfin in #902
  • Use the C++ compiler to link semigroups.so by @fingolfin in #942
  • Work around autoconf 2.69 bugs by @fingolfin in #947
  • set rpath for external libsemigroups by @dimpase in #954
  • buildsystem: sane warning if not using gmake by @james-d-mitchell in #955
• Some updates to improve the performance of LatticeOfCongruences and friends by @james-d-mitchell in #884
• Add GreensLeftMultipliers and related by @james-d-mitchell in #925

The following bugs were fixed and/or issues resolved:

• Use same URL as in my other packages by @olexandr-konovalov in #907
• Fix a few typos inn the doc by @fingolfin in #913
• Increase required version of Digraphs and remove some redundant code by @james-d-mitchell in #921
• greens: fix HClassReps(LClass) for acting semigroups by @james-d-mitchell in #927
• greens: fix bug in RightGreensMultiplier for acting semigroups by @james-d-mitchell in #930
• congsemigraph: add \= method by @james-d-mitchell in #933
• greens: fix RhoOrbStabChain(DClass) by @james-d-mitchell in #932
• doc: remove empty xml files by @james-d-mitchell in #934
• Fix a typo that breaks HPCombi support by @fingolfin in #941
• typo (ERNEL<-KERNEL) in configure.ac by @dimpase in #944
• fix the URL for libsemigroups in README.md by @dimpase in #945
• kernel: fix mem leaks by @james-d-mitchell in #951