Specify library dependencies in library.properties (#12)

Specifying the library dependencies in the depends field of library.properties causes the Arduino Library Manager (Arduino IDE 1.8.10 and newer) to offer to install any missing dependencies during installation of this library. "arduino-cli lib install" will automatically install the dependencies (arduino-cli 0.7.0 and newer).

Author: per1234

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added
+- Specify library dependencies in library.properties
 
 ## [2.0.0]
 ### Changed

library.properties

@@ -8,3 +8,4 @@ category=Display
 url=https://kamprath.net/hacks/led-matrix/
 architectures=*
 includes=LEDMatrix.h,RGBLEDMatrix.h,TimerAction.h
+depends=Adafruit GFX Library