[SX127x] Set minimum bit rate to 0.5 kbps (#665)

src/modules/SX127x/SX127x.cpp

@@ -823,10 +823,11 @@ int16_t SX127x::setBitRate(float br) {
   }
 
   // check allowed bit rate
+  // datasheet says 1.2 kbps should be the smallest possible, but 0.512 works fine
   if(_ook) {
-    RADIOLIB_CHECK_RANGE(br, 1.2, 32.768002, RADIOLIB_ERR_INVALID_BIT_RATE);      // Found that 32.768 is 32.768002
+    RADIOLIB_CHECK_RANGE(br, 0.5, 32.768002, RADIOLIB_ERR_INVALID_BIT_RATE);      // Found that 32.768 is 32.768002
   } else {
-    RADIOLIB_CHECK_RANGE(br, 1.2, 300.0, RADIOLIB_ERR_INVALID_BIT_RATE);
+    RADIOLIB_CHECK_RANGE(br, 0.5, 300.0, RADIOLIB_ERR_INVALID_BIT_RATE);
   }
 
   // set mode to STANDBY

src/modules/SX127x/SX127x.h

@@ -902,7 +902,7 @@ class SX127x: public PhysicalLayer {
     float getDataRate() const;
 
     /*!
-      \brief Sets FSK bit rate. Allowed values range from 1.2 to 300 kbps. Only available in FSK mode.
+      \brief Sets FSK bit rate. Allowed values range from 0.5 to 300 kbps. Only available in FSK mode.
 
       \param br Bit rate to be set (in kbps).