Implement async support

Refactor doctests slightly

src/lib.rs

@@ -65,29 +65,6 @@ impl Enum {
     }
 }
 ```
-```
-# use enum_from_functions::enum_from_functions;
-// `async` functions are allowed, but then all functions in the `impl` block must be `async`.
-// As well, the generated `map` function will also be `async`.
-#[enum_from_functions]
-impl Enum {
-    async fn foo() -> &'static str {
-        "Foo"
-    }
-    async fn bar() -> &'static str {
-        "Bar"
-    }
-}
-
-fn main() {
-# futures::executor::block_on(
-    async {
-        assert_eq!(Enum::map(Enum::Foo).await, "Foo");
-        assert_eq!(Enum::map(Enum::Bar).await, "Bar");
-    }
-# )
-}
-```
 ```compile_fail
 # use enum_from_functions::enum_from_functions;
 // Causes a compile error because the return types don't match.
@@ -114,6 +91,29 @@ impl Enum {
     }
 }
 ```
+`async` functions are allowed, but then all functions in the `impl` block must be `async`. The generated `map` function
+will also be `async`.
+```
+# use enum_from_functions::enum_from_functions;
+#[enum_from_functions]
+impl Enum {
+    async fn foo() -> &'static str {
+        "Foo"
+    }
+    async fn bar() -> &'static str {
+        "Bar"
+    }
+}
+
+fn main() {
+# futures::executor::block_on(
+    async {
+        assert_eq!(Enum::map(Enum::Foo).await, "Foo");
+        assert_eq!(Enum::map(Enum::Bar).await, "Bar");
+    }
+# )
+}
+```
 You can also create an empty `enum` by not providing any functions in the `impl` block (though I'm not sure why you
 would want to do this).
 ```
@@ -189,7 +189,7 @@ use syn::{
     parse_macro_input, parse_quote,
     punctuated::{Pair, Punctuated},
     token::Comma,
-    FnArg, ImplItem, Pat,
+    FnArg, ImplItem, Pat, Token,
 };
 
 /**
@@ -281,10 +281,17 @@ pub fn enum_from_functions(args: TokenStream, input: TokenStream) -> TokenStream
             }
         }));
 
+        let (await_dot, await_token) = some.asyncness.map_or((None, None), |_| {
+            (
+                Some(<Token![.]>::default()),
+                Some(<Token![await]>::default()),
+            )
+        });
+
         parse_quote! {
             pub #sig {
                 match self {
-                    #(Self::#variants => Self::#function_names(#args)),*
+                    #(Self::#variants => Self::#function_names(#args) #await_dot #await_token),*
                 }
             }
         }