The moves command writes all possible moves to the terminal.
Move the previous implementation of the moves command, which marked squares that
a piece could move to, to a 'movement' command.
Implement thiserror::Error for a bunch of error types, and remove string errors
from the implementation of the command handler in explorer.
Clean up parsing of basic types all over the place.
Update Cargo files to include thiserror and anyhow.
Clean up the implementation of the place command.
Track state with a State struct that contains a position and a builder. The place
command will place a new piece and then regenerate the position.
The make command makes a move. The syntax is:
make [color:w|b] [shape] [from square] [to square]
The fen command prints a FEN string representing the position.
