DCSS Challenge Generator 0.5 Beta

This first first beta version of DCSS Challenge Generator. Changelog:

• updated readme.md file (that one introducing repository),
• changed "Too lazy to train" challenge name to "Untrained"
• fixed including banned species, backgrounds and combos for every challenge
• added background restriction for "The Shapeless" challenge so only Transmuters and Earth Elementalism can get this challenge
• added flexibility to modify code for importing more (or less) than 3 tiers per challenge