fix(help): Use display name instead of bin name (unstable-v4)

This will mean we won't have an awkard `.exe` in the middle on Windows

This means users can have a display name for their application rather
than it being dependent on the binary name it was run as

This means users can manually set it to use spaces instead of dashes for
separating things out.

Fixes #992
Fixes #1474
Fixes #1431

src/output/help.rs

@@ -32,6 +32,15 @@ pub(crate) struct Help<'help, 'cmd, 'writer> {
 
 // Public Functions
 impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
+    #[cfg(feature = "unstable-v4")]
+    const DEFAULT_TEMPLATE: &'static str = "\
+        {before-help}{name} {version}\n\
+        {author-with-newline}{about-with-newline}\n\
+        {usage-heading}\n    {usage}\n\
+        \n\
+        {all-args}{after-help}\
+    ";
+    #[cfg(not(feature = "unstable-v4"))]
     const DEFAULT_TEMPLATE: &'static str = "\
         {before-help}{bin} {version}\n\
         {author-with-newline}{about-with-newline}\n\
@@ -40,6 +49,13 @@ impl<'help, 'cmd, 'writer> Help<'help, 'cmd, 'writer> {
         {all-args}{after-help}\
     ";
 
+    #[cfg(feature = "unstable-v4")]
+    const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
+        {before-help}{name} {version}\n\
+        {author-with-newline}{about-with-newline}\n\
+        {usage-heading}\n    {usage}{after-help}\
+    ";
+    #[cfg(not(feature = "unstable-v4"))]
     const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
         {before-help}{bin} {version}\n\
         {author-with-newline}{about-with-newline}\n\