Render partial comments.  #13

Put comment view codes from app/views/posts.html.erb to app/views/comments/_comment.html.erb.

Signed-off-by: ataka <masayuki.ataka@gmail.com>
Render partial form for adding comments.  close #13

Move a form code from posts/show.html.erb to comments/_form.html.erb.

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