Vitalize.
Licence.
Support embedded expression.
Ignore some files.
Fix circular dependency.

When run `rake test`, it reports an error:

    `Vim(let):E121: Undefined variable: s:save_cpo`

Maybe because,

1. run t/expr_parser.vim
1. source autoload/injdir/expr_parser.vim from t/expr_parser.vim
1. source autoload/injdir.vim from autoload/injdir/expr_parser.vim
1. source autoload/injdir/expr_parser.vim from autoload/injdir.vim
1. got an error