mod(structure): update project structure

Remove examples, add description for design goals in README.md and
apply re-names and naming changes accordingly for the project structure.
Implement a flat hierachry, as the library shall remain pretty simple.

src/zterm.zig

@@ -1,16 +1,19 @@
-// private imports
-
-// public import / exports
-pub const terminal = @import("terminal.zig");
 pub const App = @import("app.zig").App;
 pub const Renderer = @import("render.zig");
 
-pub const Key = terminal.Key;
-pub const Position = terminal.Position;
-pub const Size = terminal.Size;
-pub const Cell = terminal.Cell;
+pub const Cell = @import("cell.zig");
+pub const Color = @import("color.zig").Color;
+pub const Key = @import("key.zig");
+pub const Size = @import("size.zig");
+pub const Style = @import("style.zig");
 
 test {
     _ = @import("terminal.zig");
     _ = @import("queue.zig");
+
+    _ = Cell;
+    _ = Color;
+    _ = Key;
+    _ = Size;
+    _ = Style;
 }