Adds Support for Command-Line on Windows (#3699)

* + cli support on windows

- removes the preprocessor macro that prevented arg
  parsing on Windows
- adds windows-cli.cpp as src for a wrapper exe
- adds flameshot-cli target into cmake when building
  on Windows
- updates README

* updates PR

+ support for unicode characters in cli args
+ additional clarification in README re: flameshot-cli
+ new workaround for spaces in _popen path; works with relative output paths

* fix EOL

* updated flameshot.exe path construction

avoids using the hard-coded length of flameshot-cli.exe

* fix whitespace (clang)

src/main.cpp

@@ -184,7 +184,6 @@ int main(int argc, char* argv[])
         return qApp->exec();
     }
 
-#if !defined(Q_OS_WIN)
     /*--------------|
      * CLI parsing  |
      * ------------*/
@@ -609,6 +608,5 @@ int main(int argc, char* argv[])
     }
 finish:
 
-#endif
     return 0;
 }