Merge pull request #213 from zhaocai/master

Update instruction for powerline custom theme
- Improved documentation.
- Added converter_tail.
- Fixed converter_tail.
- Improved converter_relative_abbr and converter_relative_word.
- Add rec_project action
Merge pull request #214 from zhaocai/feature/rec_projecet

- Add rec_project action
- Added converter_file_directory.
- Updated a bit.
- Improved redraw_echo().
- Ver.5.1 development is started.
- Fixed load error.
Merge branch 'master' into ver.5.1
- Improved unite#convert_lines().
- Added truncate option.
Merged.
fixed document
- Fixed do_action().
Merge pull request #216 from syngan/sg-doc

fixed document
- Improved narrowing behavior.