Legend for World_map::draw().
Added world.sav to .gitignore.
Remove keybinding text, since we never use this interface anymore outside of the "Build your city here?" confirmation.  We'll probably phase this file out eventually.
input_direction() now accepts a bool (defaults to false) which determines whether it handles capital letters.  It also handles keypad entry and direction keys.
On game launch, if world.sav does not exist or we answer yes to a "Generate new world?" query, generate a new world map.  Otherwise, load from world.sav.  If we hit ESC in world.draw(), call endwin() before terminating.
New terrains: icy hill, icy mountain, glacier, and ice.  New Map_types: Icy foothills, icy mountain, and glacier.
Generation information for icy foothills, icy mountain, glacier, and icecap.
Rename TER_NULL to "Out of bounds" since that's when we'll actually see it.  Add some cabbage and amanitas to tundra (the former to be a bit nicer to arctic settlers, the latter cause it's accurate).  Data for icy hills, icy mountain, glacier, and ice.  Most terrains did not have hovels or manors listed as area options!  Added them - to most (some terrain, like swamp, are beneath the sensibilities of merchants/burghers and they won't live there).
Data for icy foothills, icy mountain, and glacier.
Add color to Mineral_datum.  New function, crop_type_color(), returns the color coding for a given Crop_type.
In arctic regions, replace rivers/canyons, hills, and mountains with glaciers, icy hills, and icy mountains - otherwise we have perfectly habitable hills among inhospitable tundra.  Improve generation status messages (no more wiggle).  Add a legend to World_map::draw() which prints location, terrain name, and crops/minerals there.  Allow simultaneous highlighting of crops and minerals.  Use input_direction() instead of a long list of direction keys.  Remove now-obsolete ? key.