Add display abstraction

In case we want to run this on something that isn't an ANSI terminal, we
have the option to implement it however we want.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

agame/display/__init__.py

@@ -0,0 +1,18 @@
+import platform
+from .display import Display
+
+if platform.system() in ("Linux", "Darwin", "Unix"):
+    from .unix import *
+
+
+class BasicDisplay(Display):
+    """
+    A basic display that should be supported on all platforms. It just outputs
+    text with some color.
+    """
+
+    def line(self, line: str = ""):
+        print(line)
+
+    def input(self) -> str:
+        return input("> ")