Feat/guide improvements

[anyanuttzilverline]

Some changes to ease the process of following the guide:

• Added fallback setting of SEQUENT_ENV to 'development' in boot.rb
• Set YAML loader to load aliases in app/database.rb
• update on PostAuthorChanged in post.rb to use field author_agregate_id rather than author
• fix minor spelling error in directory mention: app/view/layout.erb -> app/views/layout.erb