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/gas.rs

@@ -25,7 +25,7 @@ use std::time::Instant;
 
 pub fn build(ctx: &BuildContext) -> Result<f64, String> {
     let lang = ctx.language.to_lowercase();
-    if lang.split('+').any(|p| p.trim() != "asm") {
+    if lang.split(',').any(|p| p.trim() != "asm") {
         return Err("GAS backend requires build.language = \"asm\"".to_string());
     }
     let assembler = if ctx.compiler.is_empty() {