fix to compile for esp8266 on Arduino IDE
fix to compile for esp8266 on Arduino IDE

I had to remove "void Modbus::begin(long u32speed,uint8_t u8config)" method since esp8266 core implements it in another way. I dont use it so it's ok for now.

I've had to implement "void Modbus::setTxendPinOverTime( uint32_t u32overTime )" method to fix the falling edge time of the txend pin. It happens 1 byte less than needed. The user can adjust it as needed.
smarmengol/Modbus-Master-Slave-for-Arduino