fix: allow logging of a single character

[Alejandro-Casanova]

When trying to use the ArduinoLog library to print a MAC address, I used the following implementation:

   // Address stored in bd_addr is in little-endian, so should be printed 
   // backwards
   for (size_t i = 0; i < sizeof(bd_addr); i++)
   {
      size_t access_idx = sizeof(bd_addr) - 1 - i;
      if (addr.addr[access_idx] < 16)
      {
         Log.info('0');
      }
      Log.info("%x", addr.addr[access_idx]);
      if (i < sizeof(bd_addr) - 1)
      {
         Log.info(':');
      }
   }

Where the line Log.info('0'); yielded the following error:

In file included from *ommited*.cpp:12:
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h: In instantiation of 'void Logging::printLevel(int, bool, T, ...) [with T = char]':
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:270:14:   required from 'void Logging::info(T, Args ...) [with T = char; Args = {}]'
*ommited*.cpp:748:18:   required from here
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:366:22: error: no matching function for call to 'print(char&, va_list&)'
  366 |                 print(msg, args);
      |                 ~~~~~^~~~~~~~~~~
*ommited*s\Arduino\libraries\ArduinoLog/ArduinoLog.h:329:14: note: candidate: 'void Logging::print(const arduino::__FlashStringHelper*, va_list)' (near match)
  329 |         void print(const __FlashStringHelper *format, va_list args);
      |              ^~~~~
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:329:14: note:   conversion of argument 1 would be ill-formed: 
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:366:23: error: invalid conversion from 'char' to 'const arduino::__FlashStringHelper*' [-fpermissive]
  366 |                 print(msg, args);
      |                       ^~~
      |                       |
      |                       char
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:325:14: note: candidate: 'void Logging::print(const char*, va_list)' (near match)
  325 |         void print(const char *format, va_list args);
      |              ^~~~~
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:325:14: note:   conversion of argument 1 would be ill-formed: 
*ommited*\Arduino\libraries\ArduinoLog/ArduinoLog.h:366:23: error: invalid conversion from 'char' to 'const char*' [-fpermissive]
  366 |                 print(msg, args);
      |                       ^~~
      |                       |
      |                       char

It seems the library was missing the overloaded version of print to accept a single character. This is what I implemented.