Add my first interface element: a Bar!

It renders a bar of a certain width and a percentage full. Use it to render HP.

Add a new Python package called interface. The Bar class lives there. Also add a
bunch of color defintions to a module called interface.color.

erynrl/interface/bar.py

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+# Eryn Wells <eryn@erynwells.me>
+
+from . import color
+from ..geometry import Point
+
+class Bar:
+    def __init__(self, *, position: Point, width: int):
+        self.position = position
+        self.width = width
+
+        self._percent_filled = 1.0
+
+    @property
+    def percent_filled(self) -> float:
+        '''The percentage of this bar that should be filled, as a value between 0.0 and 1.0.'''
+        return self._percent_filled
+
+    @percent_filled.setter
+    def percent_filled(self, value):
+        self._percent_filled = min(1, max(0, value))
+
+    def render_to_console(self, console):
+        console.draw_rect(x=self.position.x, y=self.position.y, width=self.width, height=1, ch=1, bg=color.GREY10)
+
+        if self._percent_filled > 0:
+            filled_width = round(self._percent_filled * self.width)
+            console.draw_rect(x=self.position.x, y=self.position.y, width=filled_width, height=1, ch=1, bg=color.GREY50)

erynrl/interface/color.py

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+# Eryn Wells <eryn@erynwells.me>
+
+'''
+A bunch of colors.
+'''
+
+BLACK = (0, 0, 0)
+WHITE = (255, 255, 255)
+GREY10 = (26, 26, 26)
+GREY50 = (128, 128, 128)