style: modernize headers and refine cpplint config

- Remove legacy include guards in SystemTray.h and colorspace.h in favor of
  `#pragma once` for clarity and consistency with modern MSVC conventions.
- Stop disabling the build/header_guard cpplint rule now that guards are no
  longer needed.
- Keep resource.h excluded since it is generated by the MFC resource editor.

Author: j4y

CPPLINT.cfg

@@ -5,7 +5,7 @@ filter=-whitespace/braces,-whitespace/blank_line,-whitespace/comma,-whitespace/o
 filter=-readability/casting,-readability/braces
 
 # Disable build checks
-filter=-build/include_subdir,-build/include,-build/header_guard
+filter=-build/include_subdir,-build/include
 
 # resource.h is generated by the MFC resource editor
 exclude_files=resource.h

SystemTray.h

@@ -26,10 +26,7 @@
 // that you have found/implemented and I will fix/incorporate them into this
 // file.
 
-#ifndef _INCLUDED_SYSTEMTRAY_H_
-#define _INCLUDED_SYSTEMTRAY_H_
-
-#include <afxtempl.h>
+#pragma once
 
 /////////////////////////////////////////////////////////////////////////////
 // CSystemTray window
@@ -114,7 +111,4 @@ class CSystemTray : public CWnd
     DECLARE_MESSAGE_MAP()
 };
 
-
-#endif
-
 /////////////////////////////////////////////////////////////////////////////

colorspace.h

@@ -1,17 +1,12 @@
 // Copyright (c) 2024 Jay Prall
 // SPDX-License-Identifier: MIT
 
-
-
-#ifndef COLORSPACE_H
-#define COLORSPACE_H
+#pragma once
 
 COLORREF CMYK2RGB(BYTE c, BYTE m, BYTE y, BYTE k);
 
 void RGB2CMYK(BYTE r, BYTE g, BYTE b, BYTE& c, BYTE& m, BYTE& y, BYTE& k);
 
-
-
     BYTE    byRed = 0;
     BYTE    byGreen = 0;
     BYTE    byBlue = 0;
@@ -24,5 +19,3 @@ void RGB2CMYK(BYTE r, BYTE g, BYTE b, BYTE& c, BYTE& m, BYTE& y, BYTE& k);
     BYTE    byMagenta = 0;
     BYTE    byYellow = 0;
     BYTE    byBlack = 0;
-
-#endif //XCMYK_H