Ctags regex-based support Rust language

Hi @masatake , I have just added 'rust.c' .
For now, it is regex-based.
I have verified it by the source code of https://github.com/rust-lang/rust under Ubuntu 14.10 .
Here is the generated tags file :  https://github.com/Passw/dotfiles/blob/master/tags

No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu Utopic Unicorn (development branch)
Release:	14.10
Codename:	utopic


And also , I have modified the 'taglist.vim' plugin to support Rust language.
https://github.com/Passw/taglist.vim/commit/266fd210af26806d8ebfe64c7d0b79c1681578c2