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.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,35 @@
+---
+name: Feature Request
+about: Suggest an idea or improvement
+title: "[feat] "
+labels: enhancement
+assignees: ''
+---
+
+## Problem / Motivation
+
+<!-- What problem does this solve? What are you trying to do that's currently hard or impossible? -->
+
+## Proposed Solution
+
+<!-- Describe what you want. Be as specific as possible — CLI flags, config syntax, behavior -->
+
+## Example
+
+<!-- Show how it would look in practice (command, dcr.toml snippet, output) -->
+
+```sh
+# example command
+```
+
+```toml
+# example config
+```
+
+## Alternatives Considered
+
+<!-- Have you tried workarounds? Are there other ways to solve this? -->
+
+## Additional Context
+
+<!-- Links, prior art, related issues, etc. -->