Timer: Generic BLI_timer with Python wrapper

There is a new `bpy.app.timers` api.
For more details, look in the Python API documentation.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D3994

doc/python_api/sphinx_doc_gen.py

@@ -1842,6 +1842,7 @@ def write_rst_importable_modules(basepath):
         "bpy.app.handlers": "Application Handlers",
         "bpy.app.translations": "Application Translations",
         "bpy.app.icons": "Application Icons",
+        "bpy.app.timers": "Application Timers",
         "bpy.props": "Property Definitions",
         "idprop.types": "ID Property Access",
         "mathutils": "Math Types & Utilities",