feat: enhance build configuration with C++ standard support and variable substitution

- Added `cxx_standard` field to the build configuration for specifying C++ standards.
- Updated documentation to reflect new `cxx_standard` and variable substitution capabilities in `cflags`, `ldflags`, and `include`.
- Implemented logic to handle C++ standard flags in the build process.
- Modified object file naming to include source file extensions.
- Updated various builder modules to support new language parsing logic.
- Introduced issue and feature request templates for better community engagement.

src/core/builder/mod.rs

@@ -27,7 +27,7 @@ pub struct BuildContext<'a> {
     pub compiler: &'a str,
     pub language: &'a str,
     pub standard: &'a str,
-    #[allow(dead_code)]
+    pub cxx_standard: &'a str,
     pub target: Option<&'a str>,
     pub target_dir: Option<&'a str>,
     pub kind: &'a str,