To test this module, run
elixir test/account-test.exs
Default balance of 0:
iex(1)> account = Account.new
Optional starting balance:
iex(1)> account = Account.new(100)
iex(1)> account = Account.new(50)
iex(2)> Account.balance(account)
50
iex(1)> account = Account.new(50)
iex(2)> Account.deposit(account, 100)
iex(3)> Account.balance(account)
150
iex(1)> account = Account.new(100)
iex(2)> Account.withdraw(account, 50)
iex(3)> Account.balance(account)
50