Alchemy

[jbw3]

Alchemy!
I've added all the Alchemy cards.

Notable changes:

The big change was adding the potion cost to cards. I added a new Cost class with money and potions properties. Now all cards cost property is of type Cost. I overloaded a lot of operators for the Cost class (==, !=, <, <=, >, >=, +, -) to make logic easier, and, in most cases, this made the cost comparison logic for existing cards backwards compatible. The Cost class could also be modified to handle debt costs someday.

Alchemist and Herbalist used the Effect logic.

Possession was, of course, the most challenging to implement. I had to make a few changes to the Player class to support it.

[evanofslack]

Holy hell I missed this, checking it out now!

[evanofslack]

I had to google this, what a rabbit hole: https://boardgames.stackexchange.com/questions/10/if-possession-is-played-while-executing-another-possession-who-takes-the-next-t

[evanofslack]

Actually amazing work, this is so cool.

My only comment would be I'd prefer if the formatting/tidying changes were in a separate PR (i.e. the List -> list type changes). It doesn't really matter though, would just make it easier to review!