create dir unless article/entry

I saw http://songmu.github.io/p5-Riji/blog/entry/002_edit.html .

```
 (git)-[master]-% tree article
article
├── archives.md
├── entry
│   └── sample.md
└── index.md

 (git)-[master]-% git rm article/entry/sample.md
rm 'article/entry/sample.md'

 (git)-[master]-% git commit -m "remove sample.md"
[master 7d1e0f0] remove sample.md
 1 file changed, 1 deletion(-)
 delete mode 100644 article/entry/sample.md
```

When I ran ``git rm``, git had deleted ``article/entry``.

```
 (git)-[master]-% tree article
article
├── archives.md
└── index.md

0 directories, 2 files
```

So, it becomes an error to run the new-entry.

```
 (git)-[master]-% riji new-entry
Error sysopen on 'article/entry/2014-05-22-01.md960231865494009': No such file or directory at /Users/monmon/.anyenv/envs/plenv/versions/5.18/lib/perl5/site_perl/5.18.2/Riji/CLI/NewEntry.pm line 27.
```