Add --depth 1 option to "git submodule update"

There's no need to clone all history. Reduce build time.
Simplify AppVeyor settings
Update .gitignore

Ignore swap files and backup files.
[ci skip]
vim updated: Added tag v7-4-454 for changeset 0cdff7c26855
vim updated: Added tag v7-4-455 for changeset ebc72764fa1e
vim updated: Added tag v7-4-456 for changeset 54194bd6ed60
Build with OPTIMIZE=SPACE