added demo game in chris_demo

You had some really clear planning in your commit message--
In the "chris_demo" folder I implemented a bunch of what
you planned. I suggest playing the game I built
(go into chris_demo and run python game.py), and then
carefully reading all the source code. Then, if you like
the patterns I used, copy or move whatever you want
to use into your main project folder. Also, if there
are parts of my code you don't understand, please let
me know (in a commit message or in person next time
I'm in class) and I'll be happy to explain it.

chris_demo/card.py

@@ -0,0 +1,146 @@
+
+suits = ['♠', '♥', '♦', '♣']
+colors = ['black', 'red', 'red', 'black']
+ranks = "A23456789TJQK"
+
+class Card:
+    """A card is not an agent itself, but it manages two agents
+    which are always next to each other, representing
+    the card as something like '♠A'.
+    """
+    display = False
+
+    def __init__(self, position, index, hidden=False, selected=False):
+        """When creating a card, you pass an index, which should be a number between
+        0 and 51. If you imagine a deck of playing cards in order (all the spades from A-K, 
+        then all the hearts from A-K, etc.), then the index is all we need to identify which
+        card this is. See the CardSuit and CardRank classes below for the math we can use
+        to convert an index value to a suit or a rank.
+        """
+        self.index = index
+        self.name = str(index)
+        self.agents = [CardSuit(index, hidden, selected), CardRank(index, hidden, selected)]
+        self.set_position(position)
+
+    def __str__(self):
+        return ''.join(a.character for a in self.agents)
+
+    def __repr__(self):
+        return f"<Card {self.index} {self}>"
+
+    def value(self):
+        """Returns how many points this card is worth. Currently treats aces as worth 1. 
+        Later we might need a way of considering that an ace could be worth 1 or 11 in 
+        blackjack.
+        """
+        rank_index = self.index % 13
+        return rank_index + 1
+
+    def set_position(self, position):
+        """When the Card's position gets set, it updates
+        the position of its suit and rank. In this way, we have one 
+        agent (Card) which manages the positions of two agents on the 
+        screen.
+        """
+        x, y = position
+        suit, rank = self.agents
+        self.position = position
+        suit.position = position
+        rank.position = (x+1, y)
+
+    def set_z(self, z):
+        suit, rank = self.agents
+        suit.z = z
+        rank.z = z
+
+    def hide(self):
+        for agent in self.agents:
+            agent.hide()
+
+    def show(self):
+        for agent in self.agents:
+            agent.show()
+
+    def select(self):
+        for agent in self.agents:
+            agent.select()
+
+    def deselect(self):
+        for agent in self.agents:
+            agent.deselect()
+
+class CardSuit:
+    def __init__(self, index, hidden=False, selected=False):
+        self.name = f"{index}_suit"
+        self.index = index
+        self.suit_color = colors[index // 13]
+        self.hidden = hidden
+        self.selected = selected
+        self.update_display()
+
+    def select(self):
+        self.selected = True
+        self.update_display()
+
+    def deselect(self):
+        self.selected = False
+        self.update_display()
+
+    def show(self):
+        self.hidden = False
+        self.update_display()
+
+    def hide(self):
+        self.hidden = True
+        self.update_display()
+
+    def update_display(self):
+        if self.hidden:
+            self.character = "▒"
+            fg = "blue"
+        else:
+            self.character = suits[self.index //13]
+            fg = self.suit_color
+        if self.selected:
+            bg = "yellow"
+        else:
+            bg = "gray"
+        self.color = fg + "_on_" + bg
+
+class CardRank:
+    def __init__(self, index, hidden=False, selected=False):
+        self.name = f"{index}_rank"
+        self.index = index
+        self.suit_color = colors[index // 13]
+        self.hidden = hidden
+        self.selected = selected
+        self.update_display()
+
+    def select(self):
+        self.selected = True
+        self.update_display()
+
+    def deselect(self):
+        self.selected = False
+        self.update_display()
+
+    def show(self):
+        self.hidden = False
+        self.update_display()
+
+    def hide(self):
+        self.hidden = True
+        self.update_display()
+
+    def update_display(self):
+        if self.hidden:
+            self.character = "▒"
+            fg = "blue"
+        else:
+            self.character = ranks[self.index % 13]
+            fg = self.suit_color
+        if self.selected:
+            bg = "yellow"
+        else:
+            bg = "gray"
+        self.color = fg + "_on_" + bg