Ignore rbenv env files

Signed-off-by: ataka <masayuki.ataka@gmail.com>
Add paperclip setting in config/enviroments.  #22

Signed-off-by: ataka <masayuki.ataka@gmail.com>
Display only medium size image.  #22

Signed-off-by: ataka <masayuki.ataka@gmail.com>
Add db colums for paperclip image files.  #22

$ rails generate paperclip post image
$ rake db:migrate

Signed-off-by: ataka <masayuki.ataka@gmail.com>
New form to upload image.  #22

BUG:
If this form is submitted, I got a routing error.
```
No route matches [PUT] "/posts"
```

Signed-off-by: ataka <masayuki.ataka@gmail.com>