Simplify BCLog::Level enum class and LogLevelToStr() function

- simplify the BCLog::Level enum class (and future changes to it) by
  only setting the value of the first enumerator

- move the BCLog::Level:None enumerator to the end of the BCLog::Level
  enum class and LogLevelToStr() member function, as the None enumerator
  is only used internally, and by being the highest BCLog::Level value it
  can be used to iterate over the enumerators

- replace the unused BCLog::Level:None string "none" with an empty string
  as the case will never be hit

- add documentation

src/logging.cpp

@@ -135,7 +135,7 @@ struct CLogCategoryDesc {
 const CLogCategoryDesc LogCategories[] =
 {
     {BCLog::NONE, "0"},
-    {BCLog::NONE, "none"},
+    {BCLog::NONE, ""},
     {BCLog::NET, "net"},
     {BCLog::TOR, "tor"},
     {BCLog::MEMPOOL, "mempool"},
@@ -187,8 +187,6 @@ bool GetLogCategory(BCLog::LogFlags& flag, const std::string& str)
 std::string LogLevelToStr(BCLog::Level level)
 {
     switch (level) {
-    case BCLog::Level::None:
-        return "none";
     case BCLog::Level::Debug:
         return "debug";
     case BCLog::Level::Info:
@@ -197,6 +195,8 @@ std::string LogLevelToStr(BCLog::Level level)
         return "warning";
     case BCLog::Level::Error:
         return "error";
+    case BCLog::Level::None:
+        return "";
     }
     assert(false);
 }
@@ -206,7 +206,7 @@ std::string LogCategoryToStr(BCLog::LogFlags category)
     // Each log category string representation should sync with LogCategories
     switch (category) {
     case BCLog::LogFlags::NONE:
-        return "none";
+        return "";
     case BCLog::LogFlags::NET:
         return "net";
     case BCLog::LogFlags::TOR:

src/logging.h

@@ -68,11 +68,11 @@ namespace BCLog {
         ALL         = ~(uint32_t)0,
     };
     enum class Level {
-        Debug = 0,
-        None = 1,
-        Info = 2,
-        Warning = 3,
-        Error = 4,
+        Debug = 0, // High-volume or detailed logging for development/debugging
+        Info,      // Default
+        Warning,
+        Error,
+        None, // Internal use only
     };
 
     class Logger