Minor updates to syntax (#96)

* Update editor.h

Otherwise, compiling with header-only gives:

`gui/zep/include/zep/editor.h:439:51: error: copying member subobject of type 'std::atomic<bool>' invokes deleted constructor
    mutable std::atomic<bool> m_bPendingRefresh = true;`

* Update filesystem.cpp

* Create app_config.h

* updated conditional filesystem sourcing syntax for apple

Author: jacobfriedman

app_config.h

@@ -0,0 +1 @@
+

include/zep/editor.h

@@ -436,7 +436,7 @@ class ZepEditor
     tBuffers m_buffers;
     uint32_t m_flags = 0;
 
-    mutable std::atomic_bool m_bPendingRefresh = true;
+    mutable std::atomic_bool m_bPendingRefresh = { true };
     mutable bool m_lastCursorBlink = false;
 
     std::vector<std::string> m_commandLines; // Command information, shown under the buffer

src/filesystem.cpp

@@ -11,7 +11,12 @@
 #if defined(ZEP_FEATURE_CPP_FILE_SYSTEM)
 
 #include <filesystem>
-namespace cpp_fs = std::filesystem;
+
+#ifdef __APPLE__
+    namespace cpp_fs = std::__fs::filesystem;
+#else 
+    namespace cpp_fs = std::filesystem;
+#endif
 
 namespace Zep
 {