Fixed unaligned accesses on RP2040

This release fixes unaligned accesses on the RP2040. The compiler flags for that target somehow enabled the Cortex-M4 flags.

Fixed buffer alignment problem

This release fixes a problem when the IDAT size is smaller than the PNGdec read file size (usually 2K).

Added support for gray+alpha->RGB565

This release adds support for the pixel type "gray+alpha" (8 bit gray + 8 bit alpha value) to the getLineAsRGB565() function.

Initial Release

PNGdec is a PNG image decoder designed for MCUs with at least 48k of RAM. The features are focused on Arduino devices with a RGB565 LCD display for output.