Make widget submodules public

This will make the generated documentation more readable once I add
module docstrings. I'm still reexporting the module contents to keep
imports nice and tidy.

src/widgets.rs

@@ -1,15 +1,15 @@
-mod background;
+pub mod background;
-mod border;
+pub mod border;
-mod cursor;
+pub mod cursor;
-mod editor;
+pub mod editor;
-mod either;
+pub mod either;
-mod empty;
+pub mod empty;
-mod float;
+pub mod float;
-mod join;
+pub mod join;
-mod layer;
+pub mod layer;
-mod padding;
+pub mod padding;
-mod resize;
+pub mod resize;
-mod text;
+pub mod text;
 
 pub use background::*;
 pub use border::*;