Colourise prefix via config

[Niall47]

Config block now accepts a hash of styles to apply to the prefix.
Each component can be styled differently and an overall style applied at the end

DVLA::Herodotus.config do |c|
  c.prefix_colour = {
    system: %w[blue bold],
    date: %w[green],
    time: %w[yellow],
    correlation: %w[magenta],
    pid: %w[cyan],
    level: %w[red bold],
    separator: %w[white],
    overall: %w[underline],
  }

[BillyRuffian]

Approved -- sorry for taking so long