Possibility to set the TxPower

[TRudolphi]

I wanted to have the possibility to set the TxPower of my sensors so nearby nodes can be set to a lower power to save the batteries. I changed in my local copy of LoRaNow the following to add this (the sf was already in the lib, but I set it in the text for orientation):

LoRaNow.h:
#define LORANOW_DEFAULT_SF 7
#define LORANOW_DEFAULT_POWER 10

class LoRaNowClass : public Stream
{
private:
uint8_t sf = LORANOW_DEFAULT_SF;
uint8_t txpower = LORANOW_DEFAULT_POWER;

void setSpreadingFactor(int _sf);
void setTxPower(uint8_t _power );

LoRaNow.cpp:
void LoRaNowClass::setSpreadingFactor(int _sf)
{
sf = _sf;
}

void LoRaNowClass::setTxPower(uint8_t _power )
{
txpower = _power;
}

void LoRaNowClass::txMode()
{
LORANOW_DEBUG_PRINT(millis());LORANOW_DEBUG_PRINTLN("[ln] txMode");
LoRa.idle();
LoRa.setFrequency(frequency);
LoRa.setSpreadingFactor(sf);
LoRa.setTxPower(txpower);

==
Maybe this addition is also handy for other users.