Spelling and header fixes for the async extension.

FossilOrigin-Name: 930ba85262b76e8b1555bcfe4637135c27e04d58
diff --git a/ext/async/sqlite3async.h b/ext/async/sqlite3async.h
index 143cdc7..5b20d71 100644
--- a/ext/async/sqlite3async.h
+++ b/ext/async/sqlite3async.h
@@ -75,7 +75,7 @@
 ** On win32 platforms, this function also releases the small number of 
 ** critical section and event objects created by sqlite3async_initialize().
 */ 
-void sqlite3async_shutdown();
+void sqlite3async_shutdown(void);
 
 /*
 ** This function may only be called when the asynchronous IO VFS is 
@@ -94,7 +94,7 @@
 ** If multiple simultaneous calls are made to sqlite3async_run() from two
 ** or more threads, then the calls are serialized internally.
 */
-void sqlite3async_run();
+void sqlite3async_run(void);
 
 /*
 ** This function may only be called when the asynchronous IO VFS is