# Customizable `Proc` (with a reasonable default)
# which the Logger uses to format and print its entries.
#
# Use this setter to provide a custom formatter.
# The Logger will invoke it with the following arguments:
#  - severity: a `Logger::Severity`.
#  - datetime: `Time`, the entry's timestamp
#  - progname: `String`, the program name, if set when the logger was built
#  - message: `String`, the body of a message
#  - io: `IO`, the Logger's stream, to which you must write the output
# you want.
#
# Example:
#
# ```
# require "logger"
#
# logger = Logger.new(STDOUT)
# logger.progname = "YodaBot"
#
# logger.formatter = Logger::Formatter.new do |severity, datetime, progname, message, io|
#   label = severity.unknown? ? "ANY" : severity.to_s
#   io << label[0] << ", [" << datetime << " #" << Process.pid << "] "
#   io << label.rjust(5) << " -- " << progname << ": " << message
# end
#
# logger.warn("Fear leads to anger. Anger leads to hate. Hate leads to suffering.")
#
# # Prints to the console:
# # "W, [2017-05-06 18:00:41 -0300 #11927]  WARN --
# #  YodaBot: Fear leads to anger. Anger leads to hate. Hate leads to suffering."
# ```