Add framework for Treasure Hunt code
Landmarks class for treasure hunts

Initial creation; only case classes and support functions
Add piratey name theme to generator

Also, allow optional theme='' parameter to the namegenerator, primarily
so treasure hunts can specify only piratey names.
The 'pirate' theme is not linked to any biomes by default, so will not
currently appear unless specifically requested.  Possibly it could be
given a non-zero chance on beach and island biomes (25, 26, 14, 15, 16)
though it may not be compatible with the current entrance styles and so
is not enabled for now
Support functions for treasure hunts

Adds optional 'note' parameter to worldmap; adds keyName generator in
dungeon class;  adds materialById function in materials; adds
encodeTHuntInfo function in utils.  Also allows decodeDungeonInfo to
recognise books by new named ID as well as numerical.
Change landmarks to use absolute voxels

Landmarks class holds locations in absolute voxels, rather than
relative.  Default landmark changed to Clearing. Chest placing fixed and
more landmark rendering added.
Add mcdungeon commands for Treasure Hunts

Add support for treasure hunts to the main interface.  Added 'addth'
command; added treasure hunts to 'interactive', 'list' and 'genpoi', as
well as to 'delete' and 'regenerate'.
Working treasure hunts at last

Still need to do more landmarks; investigate delete and regenerate
behaviour; proper burying of Thunt data cache
Add more landmarks, fix key handling

Fix key problems
Add monolith
Fix rendering of cottage
Make debug info only printed in debug mode
Add progress bar for chest placement
Add spawners in treasure hunt landmarks.

Since these are on the surface, spawned monsters should be able to
survive in daylight.  Spiders, skeletons with helmets, enraged pigmen,
etc.
Change config to use a separate section

Using a th_ prefix is messy.  Have a separate section in the config file
instead.

Also add new Memorial landmark type
Add biomes to landmarks, improve rendering

Change stone type for biome
Check for liquids in landmark chunk
Attempt to erase trees in the clearing by working upwards
More debug outputs
Make book 1.8 compatible (may need to be backed out)
Force thunt cache chest to be at y=-128
Merge in Upstream changes

Merge in all upstream changes from orphu/development
Add icons for overviewer POI configuration
Merge branch 'development' of https://github.com/sshipway/mcdungeon into sshipway-development
Merge branch 'sshipway-development' into development