* new ESPNOWRadio driver

* refactored the examples/*/main.cpp modules, moving radio specifics to variants/*/target modules
* new Generic_ESPNOW_* target envs

variants/heltec_v2/target.cpp

@@ -10,6 +10,8 @@ HeltecV2Board board;
   RADIO_CLASS radio = new Module(P_LORA_NSS, P_LORA_DIO_1, P_LORA_RESET, P_LORA_BUSY);
 #endif
 
+WRAPPER_CLASS radio_driver(radio, board);
+
 #ifndef LORA_CR
   #define LORA_CR      5
 #endif
@@ -29,3 +31,23 @@ bool radio_init() {
   
   return true;  // success
 }
+
+uint32_t radio_get_rng_seed() {
+  return radio.random(0x7FFFFFFF);
+}
+
+void radio_set_params(float freq, float bw, uint8_t sf, uint8_t cr) {
+  radio.setFrequency(freq);
+  radio.setSpreadingFactor(sf);
+  radio.setBandwidth(bw);
+  radio.setCodingRate(cr);
+}
+
+void radio_set_tx_power(uint8_t dbm) {
+  radio.setOutputPower(dbm);
+}
+
+mesh::LocalIdentity radio_new_identity() {
+  RadioNoiseListener rng(radio);
+  return mesh::LocalIdentity(&rng);  // create new random identity
+}