Start 3.5.1

Due to a misconfigured tool, an incorrect 3.5.0 tag was briefly made
available in the main Git repository.  Thanks to the manual intervention
of many packaging volunteers this has been almost entirely rolled back.
To make sure this release supersedes the incorrect tag everywhere, the
first release of GLFW 3.5 is named 3.5.1.

There are no code changes other than the version patch number.

Fixes #2758

README.md

@@ -118,6 +118,10 @@ guide](https://github.com/glfw/glfw/blob/master/docs/CONTRIBUTING.md) for
 information on what to include when reporting a bug.
 
 
+## Changelog since 3.5
+
+None.
+
 ## Changelog since 3.4
 
  - Added `GLFW_UNLIMITED_MOUSE_BUTTONS` input mode that allows mouse buttons beyond