WIP Level system

[jrambold]

Adds an exponential level system
XP Gains and checks made at the end of battle
XP Gain PvP based of percent xp needed to level up and level difference between opponents
XP Gain PvE based on monster xp set
Stat growth currently randomized at 8-12% per stat (growth currently effected by items)

Currently no class system

As leveling, xp, and stat growth can play a large function is there an overall place that would be good to set those rates?
Does this sound like a generally solid rate for level growth?

Additional testing is still needed. I wanted to check on the structure of the additions before continuing.

[nskins]

Hi @jrambold - thank you for opening this pull request. It looks like things are off to a good start, but I'd urge you to think about/write more testing before implementing this.

As leveling, xp, and stat growth can play a large function is there an overall place that would be good to set those rates?

Those would likely be member variables of a Class in the class system, so it's fine to hard code the values on our first draft.

Does this sound like a generally solid rate for level growth?

I'm not exactly sure, but it can be updated later if need be.

The most important thing, in the long-term, will be that these rates & algorithms can be set by the user of the Goby framework via something like a Class.

Also, you will need to update the base branch of your pull request to 0.2.1 as I do not accept pull requests directly to master. Thanks!