Version 0.3.1

New features and new API:

• Added Alda::NREPLServerError#status.
• Added Alda::env.
• Alda::down? and Alda::up? is now useful in Alda 2.
• Added Alda::REPL#reline.

BREAKING changes of API:

• Now status should be specified as a parameter of Alda::NREPLServerError::new.

Fixed bugs:

• Fixed: alda-irb does not run correctly in Ruby 3.
• Fixed: cannot handle unknown-op error of nREPL server.
• Fixed: an excess message printed when exiting REPL on Windows.

Other changes:

• Fixed dependencies.
• Fixed some changelog of 0.3.0.
• Added a gem badge in README.
• Updated bundler version.