Add example games and quick-start guide

Two example .ne programs with compiled .nes ROMs:
- hello_sprite: d-pad controlled sprite movement
- bouncing_ball: auto-bouncing sprite with edge detection

Includes README with build instructions and emulator setup.

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

examples/README.md

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+# NEScript Examples
+
+## Quick Start
+
+### 1. Build the compiler
+
+```
+cargo build --release
+```
+
+### 2. Compile an example
+
+```
+cargo run -- build examples/hello_sprite.ne
+```
+
+This produces `examples/hello_sprite.nes` — a valid iNES ROM file.
+
+### 3. Run in an emulator
+
+Open the `.nes` file in any NES emulator:
+
+- **[Mesen](https://www.mesen.ca/)** (recommended — best debugging support)
+- **[FCEUX](https://fceux.com/)**
+- **[Nestopia](http://nestopia.sourceforge.net/)**
+
+Use the d-pad (arrow keys in most emulators) to move the sprite.
+
+## Examples
+
+| File | Description |
+|------|-------------|
+| `hello_sprite.ne` | Move a smiley face with the d-pad |
+| `bouncing_ball.ne` | A sprite that bounces around the screen automatically |
+
+## What you'll see
+
+The ROM displays a small smiley-face sprite (an 8x8 tile built into the
+compiler's default CHR data). In `hello_sprite`, you control it with the d-pad.
+In `bouncing_ball`, it moves on its own and bounces off the screen edges.
+
+## Emulator controls
+
+| NES Button | Typical Key |
+|------------|-------------|
+| D-pad      | Arrow keys  |
+| A          | Z           |
+| B          | X           |
+| Start      | Enter       |
+| Select     | Right Shift |
+
+(Exact mappings vary by emulator — check your emulator's input settings.)
+
+## Compiler commands
+
+```
+# Compile to ROM
+cargo run -- build examples/hello_sprite.ne
+
+# Compile with custom output path
+cargo run -- build examples/hello_sprite.ne --output my_game.nes
+
+# Type-check only (no ROM output)
+cargo run -- check examples/hello_sprite.ne
+```