Support for colorized output

[solnic]

This restores colorize: true option and introduces support for color tags in string templates.

Supported colors:

COLORS = {
  black: 30,
  red: 31,
  green: 32,
  yellow: 33,
  blue: 34,
  magenta: 35,
  cyan: 36,
  gray: 37
}.freeze

Here are a couple of usage examples:

# to enable coloring of severity
logger = Dry.Logger(:test, colorize: true)

# to enable customize severity colors
logger = Dry.Logger(:test, colorize: true, severity_colors: {info: :blue})

# to use colors in templates
logger = Dry.Logger(:test, template: "<green>%<message>s</green>")