Tiny fixes and refactorings

- autoload/hatenablog.vim
    - removed trailing spaces
    - removed useless ':'
    - used a number for getline()
    - improved redundant expression in s:validateConfig()

- plugin/hatenablog.vim
    - fixed load-guard variable name
    - removed cpo-save because line continuation doesn't exist. please
      see :help use-cpo-save