Refine Admin panel (boards and posts)
字串改雙引號、form_for 改成新寫法、讀attribute不加self.
link_to 加上括號
Merge branch 'refactoring-coding-style'

Conflicts:
	app/views/admin/boards/index.html.erb
	app/views/admin/boards/show.html.erb
	app/views/admin/posts/new.html.erb
	app/views/admin/posts/show.html.erb
	app/views/boards/show.html.erb
	app/views/posts/show.html.erb