mana: add mana field, add mana vision (press 'm')

Signed-off-by: mkhropov <mkhropov@gmail.com>
iface: make 2D cursor a bit prettier

Signed-off-by: mkhropov <mkhropov@gmail.com>
biomes: reorganize slightly. Going to make more subfolders later

Signed-off-by: mkhropov <mkhropov@gmail.com>
renderer: FK forgot to actually include drawing code for manaField

Signed-off-by: mkhropov <mkhropov@gmail.com>