message: doc: update enum naming in developer notes
  Update the enumerator examples to snake_case per CPP Core Guidelines
  Clarify that in this project enumerators may be snake_case, PascalCase, or
  ALL_CAPS, and to use what is seems appropriate.
diff: @@ -89,6 +89,10 @@ code.
  - Class member variables have a `m_` prefix.
  - Global variables have a `g_` prefix.
  - Constant names are all uppercase, and use `_` to separate words.
  + - Enumerator constants may be `snake_case`, `PascalCase` or `ALL_CAPS`.
  + This is a more tolerant policy than the [C++ Core
  + Guidelines](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Renum-caps),
  + which recommend using `snake_case`. Please use what seems appropriate.
  - Class names, function names, and method names are UpperCamelCase
  (PascalCase). Do not prefix class names with `C`.
  - Test suite naming convention: The Boost test suite in file
  @@ -668,19 +672,19 @@ Foo(vec);
  ```cpp
  enum class Tabs {
  - INFO,
  - CONSOLE,
  - GRAPH,
  - PEERS
  + info,
  + console,
  + network_graph,
  + peers
  };
  int GetInt(Tabs tab)
  {
  switch (tab) {
  - case Tabs::INFO: return 0;
  - case Tabs::CONSOLE: return 1;
  - case Tabs::GRAPH: return 2;
  - case Tabs::PEERS: return 3;
  + case Tabs::info: return 0;
  + case Tabs::console: return 1;
  + case Tabs::network_graph: return 2;
  + case Tabs::peers: return 3;
  } // no default case, so the compiler can warn about missing cases
  assert(false);
  }
  