Write the coding-style guide for Modmesh

CODINGSTYLE.md

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+# Coding Style
+
+## Naming
+
+1. Class names use CamelCase, for example: `class CallProfiler;`.
+   - Qt-related classes prepend an additional `R`, like `class RLine;`.
+     * A class is considered Qt-related if its parent class belongs to the Qt library.
+
+2. Variable names and using-declarations use snake_case:
+   - Example variable: `R3DWidget * viewer;`
+   - Example using-declaration: `using size_type = std::size_t;`
+
+3. Qt-related function names use CamelCase, while non-Qt-related function names use snake_case.
+   - Functions are Qt-related if they belong to a Qt-related class.
+   - Example Qt-related function: `QMdiSubWindow * RManager::addSubWindow(Args &&... args);`
+   - Example non-Qt-related function: `void initialize_buffer(pybind11::module & mod);`
+
+4. Class members begin with `m_`.
+
+5. [Macros](https://en.cppreference.com/w/cpp/preprocessor/replace) start with `MM_DECL_`.
+
+6. [Using-declarations](https://en.cppreference.com/w/cpp/language/using_declaration) end with `_type`.
+
+7. Acronyms within names should be treated as words instead of using ALL_CAPS_CONSTANTS.
+   - Example classes: `class HttpRequest;`
+   - Example function: `void update_geometry_impl(StaticMesh const & mh, Qt3DCore::QGeometry * geom);`
+
+Certainly! Here's a more coherent version:
+
+## Comments
+
+1. Comment blocks should follow [Doxygen style guidelines](https://www.doxygen.nl/manual/docblocks.html).
+
+2. For one-line comments like `/* end of NamespaceOrClassName */`, 
+   place them at the end of namespaces or classes.  
+   Example usage:
+   ```c++
+   namespace modmesh
+   {
+   // More code...
+   }; /* end of modmesh */
+   ```
+
+3. It is highly recommended to include references in comment blocks.
+
+## Formatting
+
+1. Ensure there is a blank line between the definitions of classes and functions.
+
+2. Long lines should be divided into shorter ones.
+   - For C++, no specific line length limit is set.
+   - For Python, adhere to an 80-character limit per line.
+
+## Class
+
+1. It's advisable to explicitly define constructors and destructors for classes whenever possible.