Upgrade Rust dependencies and add build (#55)

Add nimber evaluation benchmarks

Upgrade to Criterion 0.4 (#54)

Update to Rust 2021

cargo fix

Add benchmark instructions

cargo update

Use Vec::with_capacity in CompoundPosition.legal_moves (#49)

Two more uses of iteration pattern (#49)

More use of width() and height()

Iteration pattern in is_end_of_game (#49)

Use Vec::with_capacity in SimplePosition.legal_moves (#49)

Factor out set_string_value

Use width() and height() functions

Add more benchmarks