Feature: Items that can increase a power's upgrade level

[dorkster]

It would be nice if we could have items that have something like "+1 to Blood Strike". One thing to consider is if such a bonus would require the base level power to already be unlocked. Maybe have a flag that let's use set that. Syntax could look like this:

# requires Blood Strike (Level 1)
bonus_power_level=7,false

# will unlock Blood Strike (Level 1) if it is not already unlocked
bonus_power_level=7,true