Driver for the switch-science "I2C 8x8 LED matrix" board (https://www.switch-science.com/products/2071), which multiplexes an 8x8 LED matrix over I2C using the PCA9622 constant-current LED driver.

start_link/1 accepts:

• :bus_name - the I2C bus to open (default: "i2c-2")
• :i2c_address - the PCA9622's I2C address (default: 0x50)
• :reflesh_interval - column refresh interval in ms (default: 10)
• :initial_matrix - initial 8x8 matrix to display
• :name - GenServer name to register under (default: PCA9622Matrix8x8); pass nil to start unnamed, which allows multiple boards to run at once. When a name other than the default is used (or nil), pass the returned pid/name explicitly to set_matrix/2, set_matrix_bit/4, set_interval/2 and stop/1.