split Board.place into 'resize' and 'place'
fix board remove piece
fix Board.place
add direction constants
Hive.one_hive suport to stacked pieces
move 'place piece' validation logic
keep the 'pieces on board' state in the Hive class
fix the shell client when placing the first piece
Revert "fix board remove piece"

This reverts commit 2d7361832d2e55540ceb8a4697f45cad986eb267.
draft implementation of Hive.move_piece
refactor Hive.place_piece
use new API from shell client
add TODO file
beautify README
Update README.md