Introduced two "somewhat scale-free" normalization options sqrt_max and max_min_sqrt_max, #20
Updated hass-entso-e default entity to sensor.average_electricity_price_today which is the only entity providing prices attribute in hass-entso-e v0.1.2+
Compatible with https://github.com/JaccoR/hass-entso-e/releases/tag/v0.1.3-hotfix