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/unix.py

@@ -0,0 +1,88 @@
+import sys
+import termios
+from typing import Optional, TextIO
+from agame.color import colorize
+from .display import Display
+
+ESC = "\u001b"
+ANSI_MOVE_BOTTOM = f"{ESC}[999;0f"
+
+
+class ANSIDisplay(Display):
+    """
+    Display for a modern terminal.
+
+    This display attempts to keep the input at the bottom, and the output
+    scrolling up.
+
+    This utilizes `termios` and is therefore UNIX-only.
+    """
+
+    def __init__(
+        self,
+        input_prompt: str = colorize("{{>}} "),
+        stdin: TextIO = sys.stdin,
+        stdout: TextIO = sys.stdout,
+    ):
+        self.input_prompt = input_prompt
+        self.__stdin = stdin
+        self.__stdout = stdout
+        # Initial set-up:
+        # . Move the cursor to the bottom left part of the screen (this will set
+        #   the current line to a really high value and will move us to the
+        #   bottom of the screen)
+        self.stdout.write(ANSI_MOVE_BOTTOM)
+
+        # . Disable echo, set cbreak
+        fd = self.stdin.fileno()
+        self.__old_attrs = termios.tcgetattr(fd)
+        self.cbreak()
+
+        # . Clear
+        self.clear()
+
+    def line(self, line: str = ""):
+        self.stdout.write(line)
+        self.stdout.write("\n")
+
+    def input(self) -> str:
+        try:
+            self.nocbreak()
+            return input(self.input_prompt)
+        finally:
+            self.cbreak()
+
+    def wait_for_ack(self, prompt: Optional[str] = "Press any key to continue..."):
+        # Flush unread data
+        termios.tcflush(self.stdin.fileno(), termios.TCIFLUSH)
+        if prompt is not None:
+            self.line(prompt)
+        self.stdin.read(1)
+
+    def cbreak(self):
+        fd = self.stdin.fileno()
+        new = termios.tcgetattr(fd)
+        new[3] &= ~(termios.ECHO | termios.ICANON)
+        termios.tcsetattr(fd, termios.TCSADRAIN, new)
+
+    def nocbreak(self):
+        fd = self.stdin.fileno()
+        new = termios.tcgetattr(fd)
+        new[3] |= termios.ECHO | termios.ICANON
+        termios.tcsetattr(fd, termios.TCSADRAIN, new)
+
+    def finish(self):
+        # Clean up by restoring the old terminal state
+        fd = self.stdin.fileno()
+        termios.tcsetattr(fd, termios.TCSADRAIN, self.__old_attrs)
+
+    def clear(self):
+        self.stdout.write(f"{ESC}[2J")
+
+    @property
+    def stdin(self) -> TextIO:
+        return self.__stdin
+
+    @property
+    def stdout(self) -> TextIO:
+        return self.__stdout