v0.21: Buff your coins with stamps

# Added stamps

Stamps are buffs you can add to a coin. Coins can have multiple stamps, but not more than one of each kind. When 2 coins merge, any stamps they were carrying get combined into the newly formed coin.

Stamps can be bought with Lids which are a meta-currency that is acquired by dropping coins. There may be more ways to get lids in the future, such as by doing activities in the ventures.

Here are the 5 kinds of stamps:

## Double Merge Bonus

Doubles the currency gained when the coin merges.

## Increase Value

Adds 50 to the value of the coin. This amount can be upgraded.

## Insurance Policy

If this coin falls out of the jar, it will respawn with all stamps intact (except Insurance Policy).

## Lucky

25% chance to skip a tier when merging.

## Fragile

50% chance to break when merging. When it breaks, earn the value multiplied by the number of times it cheated death.

# Other changes

Powers have been changed to cost PP (power points). You gain PP by merging coins. This change should allow using powers at a consistent pace throughout your gameplay.