Windows support

- Vim bootstrap version(number in first line): Just got it from the website today
- Operating system: Windows Server 2019
- Vim/Nvim version: gvim 8.1.1
- Languages: C, python, Go

I can get gvim to open with the vim-bootstrap configuration, but only if I edit the `.vimrc` file, replacing a couple of paths:

```vim
let vimplug_exists=expand('~/./autoload/plug.vim')

" ... skip a few lines

call plug#begin(expand('~/./plugged'))
```

to
```vim
let vimplug_exists=expand('~/vimfiles/autoload/plug.vim')

" ... skip a few lines

call plug#begin(expand('~/vimfiles/plugged'))
```

When I then call gvim from powershell, the plug-ins will install. However nothing works when I start the initial launch from git bash.

One thing I've noticed is that a number of the plug-ins don't work on Windows - such as git-gutter (messages about being unable to open temporary files in `C:/Users/user/AppData/Local/Temp/5/RandChars.tmp` while processing 143_git_supports_command_line_config_override) and ultisnips (constant reminders that it needs python installed).

Once they're out of the way I've found the system to be quite usable. Perhaps those plug-ins should be disabled if the user selects Windows for their OS?