Merge pull request #146 from ujihisa/master

more documented
- Added source custom variables.
tweak <Plug>(unite_delete_backward_path) to exit when no string on prompt

Like <Plug>(unite_delete_backward_char) .
Merge pull request #147 from tyru/unite-delete-backward-path

<Plug>(unite_delete_backward_path)もプロンプトに入力がない時はuniteを終了させるようにしました
- Deleted comment out.
- Improved mkdir action.
- Mereged.
- Added backup action.
- Added unite#util#system_passwd().
- Fixed unite#get_default_action().
- Fixed print default_action.
- Improved max_width.
- Improved update behavior.
- Fixed error.
improves the documentation a bit
improves the usage and install section
small documentation improvements
Merge pull request #150 from cpfaff/doc_improvement

Documentation english improvement
Improves english documentation
improves the documentation english