Create dragon.rb

Small command-line game I (partially) wrote. I added a level system, with increasing ammount of experience (need/gain) per level. Also you gain stats (strength/hitpoints/stamina) with every level. I added a work function, which allows you to gain experience and find items (you can also find items while walking). We keep track of time and there's a couple more things. Anyway this is was just a project to get a better understanding of Ruby. I will change and improve some things for sure, any suggestions welcome.