feat: call telescope without load_extension (#75)

With this patch, you can call `:Telescope possession` when you have not
called `telescope.load_extension()` before.

See nvim-telescope/telescope.nvim#2655

NOTE: You still need to call `load_extension()` for calling
`telescope.extensions.possession.list()` / `.possession()`.

lua/telescope/_extensions/possession.lua

@@ -4,5 +4,6 @@ local pickers = require('possession.telescope')
 return telescope.register_extension {
     exports = {
         list = pickers.list,
+        possession = pickers.list,
     },
 }