Added converter functions for Experience points and levels

[zisis912]

These two functions allow someone to easily calculate how many xp points a certain amount of xp levels equate to, and vice versa.

I know it sounds dumb easy but considering it needs exponents and square roots and stuff I thought why not.

[rom1504]

duplicate of #3124

[zisis912]

@rom1504 This is not a duplicate, it is a completely different function. What #3124 does is get the total xo.the bot has.

These functions help someone convert levels to points and vice versa.

For example, convertLevelsToXpPoints(30) returns 1395 and convertXpPointsToLevels(1395) does the exact opposite.

This function has a parameter unlike #3124, I would suggest you check the file changes to get a better idea of what this is