Fix compilation errors for modern Xcode versions

- Fix incompatible function pointer types in LinkingEditor.m by adding explicit IMP cast
- Fix incompatible function pointer types in GlobalPrefs.m by adding explicit cast
- Remove deprecated -whatsloaded linker flag from project settings

These changes allow the project to build successfully on Xcode 16 with macOS SDK 26.2.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Revert "Add support for Markdown (.md and .markdown) files"

This reverts commit 1c0f2d9.

Revert "Add support for Markdown (.md and .markdown) files"

This reverts commit 1c0f2d9.