Test: ignore emacs backup file as input of unit test cases

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
add regex parser for RUST language

It is taken from https://github.com/Passw/dotfiles/blob/master/rust.ctags.

TODO: corpus and test cases
add a very basic test case for rust parser

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
write about the parsers for rust language, mib, ctags optlib

Signed-off-by: Masatake YAMATO <yamato@redhat.com>