Integrated vim-spellsync

Magically rebuild Vim spell files if word lists are modified outside of
Vim. One use case would be if word lists are stored in a source control
system like Git and shared across multiple computers\. SpellSync also
creates `.gitignore` and `.gitattributes` files in Vim's spell directories
to exclude binary spell files and uses its union merge driver to avoid
conflicts.
[link]](https://github.com/micarmst/vim-spellsync)

.vim/spell/.gitattributes

@@ -0,0 +1 @@
+*.add merge=union