Embedded-UART-SPS 3.0.0

 * [`added`]   Multiple sensors API `sensirion_uart_select_port`
 * [`added`]   Multiple sensors sample implementation for arduino MKR0
 * [`changed`] Split out `default_config.inc` from Makefile to
configure paths
               and CFLAGS
 * [`fixed`]   Fix strict-aliasing ans sign-conversion compiler
warnings
 * [`added`]   instantly start manual fan cleaning with
               `sps30_start_manual_fan_cleaning()`
 * [`changed`] rename `SPS_*` constants to `SPS30_`