enable gtk frontend in windows (#58)

The gtk frontend can now be built in windows!
The github workflow is updated to build GTK and add it to the releases section.

src/frontend.rs

@@ -31,16 +31,16 @@ use crate::{
 pub mod cli;
 
 /// gtk frontend
-#[cfg(all(unix, feature = "gtk"))]
+#[cfg(feature = "gtk")]
 pub mod gtk;
 
 pub fn run_frontend(config: &Config) -> Result<()> {
     match config.frontend {
-        #[cfg(all(unix, feature = "gtk"))]
+        #[cfg(feature = "gtk")]
         Frontend::Gtk => {
             gtk::run();
         }
-        #[cfg(any(not(feature = "gtk"), not(unix)))]
+        #[cfg(not(feature = "gtk"))]
         Frontend::Gtk => panic!("gtk frontend requested but feature not enabled!"),
         Frontend::Cli => {
             cli::run()?;