Move glyph definitions into a central type

pkg/atlas/glyph.go

@@ -0,0 +1,27 @@
+package atlas
+
+// Glyph represents the text representation of something in the game
+type Glyph byte
+
+const (
+	// GlyphNone is a keyword for nothing
+	GlyphNone = Glyph(0)
+
+	// GlyphRock is solid rock ground
+	GlyphRock = Glyph('-')
+
+	// GlyphGravel is loose rocks
+	GlyphGravel = Glyph(':')
+
+	// GlyphSand is sand
+	GlyphSand = Glyph('~')
+
+	// GlyphRover represents a live rover
+	GlyphRover = Glyph('R')
+
+	// GlyphSmallRock is a small stashable rock
+	GlyphSmallRock = Glyph('o')
+
+	// GlyphLargeRock is a large blocking rock
+	GlyphLargeRock = Glyph('O')
+)