Use subject.method instead of Tumblfetch::CLI.new.invoke('method')
Use say(Thor::Actions) instead of puts
Reduce nest of describe
Print message to stdout instead of stderr

ひとまず全部stdoutに出力する。stderrとの使い分けは必要になったら考える。
Use let for remove repetition
Remove needles './'
Use output(is capture stdout) for remove needless output
Use stub instead of File.open. Don't create needless file.
Remove needless constant
Strict stub, and add check for generating .tumblfetch
Extract stub to before block
Use subject
Merge pull request #3 from senosa/refactoring-cli-spec

Refactoring CLI spec