Add more sample codes for API

[joseluisq]

I suggest to add more sample codes and details for each API function.

• Load example - b5761a6
• Resize example - b5761a6
• Crop example - b5761a6
• Rotate example - b5761a6
• Line-height example - b5761a6
• Text example - b5761a6
• Figure example - b5761a6