The settings were modified to be simpler

- Modbus.h was isolated in two files: ModbusDefinitions (with type
definitions and etc) and ModbusSettings.h (General settings for Modbus)
- The plataform settings permits faster modification on LSPCLK and
CPU_FREQ (you can use it only for modbus, or you can use it for your
whole project)
- Serial configs now are at ModbusSettings