Restore after/syntax/rust.vim (conceal)
Restore after/syntax/rust.vim (conceal)

It was a casualty of war in the merge to Vim: it took on the form of
syntax/rust.vim, losing its own nature and contents.

This restores conceal functionality. I don’t use it myself but clearly
at least one person uses it!

Fixes #167

rust-lang/rust.vim