Add editors/vim-tiny.

By popular request, this is a slave port that installs only the vim binary. It has
no dependencies, produces a 1 MB package with a 3 MB installed footprint, and
is unable to do anything except edit files. It contains no help files, no runtime
files, no syntax highlighting, no filetype-specific indenting, non-US keymaps,
macros, or spell-checking.

vim-tiny is designed for minimal installs, and is the wrong choice for most users.