use c++17

version bump

Allow passing docid as string instead of bytes #26

For backward-compatibility, passing bytes is still allowed as well

updated dependencies for frog 0.31

macosx wheel building: compile against homebrew's 'keg-only' libxml2 …

…and icu4c

version bump for compilation against frog v0.30

metadata update

version bump for compilation against ucto v0.28

wheels broke again? try install libxml2 in same prefix as the rest

dependency update: frog >= 0.26