Rewrite KISS modem to be fully spec-compliant

variants/xiao_nrf52/platformio.ini

@@ -107,4 +107,13 @@ build_flags =
 ;  -D MESH_PACKET_LOGGING=1
 ;  -D MESH_DEBUG=1
 build_src_filter = ${Xiao_nrf52.build_src_filter}
-  +<../examples/simple_room_server/*.cpp>
+  +<../examples/simple_room_server/*.cpp>
+
+[env:Xiao_nrf52_kiss_modem]
+extends = Xiao_nrf52
+build_flags =
+  ${Xiao_nrf52.build_flags}
+build_src_filter = ${Xiao_nrf52.build_src_filter}
+  +<../examples/kiss_modem/*.cpp>
+lib_deps =
+  ${Xiao_nrf52.lib_deps}