Added categories

README.md

app/assets/stylesheets/category.scss

app/controllers/application_controller.rb

app/controllers/category_controller.rb

app/controllers/post_controller.rb

app/helpers/category_helper.rb

app/models/blog.rb

app/models/category.rb

app/models/post.rb

app/views/category/get.html.erb

app/views/category/manage.html.erb

app/views/post/edit.html.erb

app/views/post/new.html.erb

app/views/posts/_post.html.erb

app/views/user/dashboard.html.erb

config/routes.rb

db/migrate/20200322145832_create_categories.rb

db/schema.rb

test/controllers/category_controller_test.rb

test/fixtures/categories.yml